diff --git a/problem_builder/mcq.py b/problem_builder/mcq.py
index 6080c173..f58e7f1d 100644
--- a/problem_builder/mcq.py
+++ b/problem_builder/mcq.py
@@ -99,7 +99,7 @@ def calculate_results(self, submission):
 
         return {
             'submission': submission,
-            'message': self.message,
+            'message': self.message_formatted,
             'status': 'correct' if correct else 'incorrect',
             'tips': formatted_tips,
             'weight': self.weight,
diff --git a/problem_builder/mentoring.py b/problem_builder/mentoring.py
index 8024d8a7..39edbde4 100644
--- a/problem_builder/mentoring.py
+++ b/problem_builder/mentoring.py
@@ -99,6 +99,13 @@ class BaseMentoringBlock(
         scope=Scope.content,
         enforce_type=True
     )
+    weight = Float(
+        display_name=_("Weight"),
+        help=_("Defines the maximum total grade of the block."),
+        default=1,
+        scope=Scope.settings,
+        enforce_type=True
+    )
 
     # User state
     num_attempts = Integer(
@@ -109,6 +116,7 @@ class BaseMentoringBlock(
     )
 
     has_children = True
+    has_score = True  # The Problem/Step Builder XBlocks produce scores. (Their children do not send scores to the LMS.)
 
     icon_class = 'problem'
     block_settings_key = 'mentoring'
@@ -197,8 +205,11 @@ def publish_event(self, data, suffix=''):
         Publish data for analytics purposes
         """
         event_type = data.pop('event_type')
-        self.runtime.publish(self, event_type, data)
+        if (event_type == 'grade'):
+            # This handler can be called from the browser. Don't allow the browser to submit arbitrary grades ;-)
+            raise JsonHandlerError(403, "Posting grade events from the browser is forbidden.")
 
+        self.runtime.publish(self, event_type, data)
         return {'result': 'ok'}
 
     def author_preview_view(self, context):
@@ -214,6 +225,10 @@ def author_preview_view(self, context):
         self.include_theme_files(fragment)
         return fragment
 
+    def max_score(self):
+        """ Maximum score. We scale all scores to a maximum of 1.0 so this is always 1.0 """
+        return 1.0
+
 
 class MentoringBlock(BaseMentoringBlock, StudioContainerXBlockMixin, StepParentMixin):
     """
@@ -262,13 +277,6 @@ class MentoringBlock(BaseMentoringBlock, StudioContainerXBlockMixin, StepParentM
     )
 
     # Settings
-    weight = Float(
-        display_name=_("Weight"),
-        help=_("Defines the maximum total grade of the block."),
-        default=1,
-        scope=Scope.settings,
-        enforce_type=True
-    )
     display_name = String(
         display_name=_("Title (Display name)"),
         help=_("Title to display"),
@@ -323,8 +331,6 @@ class MentoringBlock(BaseMentoringBlock, StudioContainerXBlockMixin, StepParentM
         'display_submit', 'feedback_label', 'weight', 'extended_feedback'
     )
 
-    has_score = True
-
     @property
     def is_assessment(self):
         """ Checks if mentoring XBlock is in assessment mode """
@@ -377,10 +383,6 @@ def score(self):
 
         return Score(score, int(round(score * 100)), correct, incorrect, partially_correct)
 
-    def max_score(self):
-        """ Maximum score. We scale all scores to a maximum of 1.0 so this is always 1.0 """
-        return 1.0
-
     def student_view(self, context):
         # Migrate stored data if necessary
         self.migrate_fields()
@@ -645,7 +647,7 @@ def submit(self, submissions, suffix=''):
             # Save the user's latest score
             self.runtime.publish(self, 'grade', {
                 'value': self.score.raw,
-                'max_value': 1,
+                'max_value': self.max_score(),
             })
 
             # Mark this as having used an attempt:
@@ -712,7 +714,7 @@ def handle_assessment_submit(self, submissions, suffix):
             log.info(u'Last assessment step submitted: {}'.format(submissions))
             self.runtime.publish(self, 'grade', {
                 'value': score.raw,
-                'max_value': 1,
+                'max_value': self.max_score(),
                 'score_type': 'proficiency',
             })
             event_data['final_grade'] = score.raw
@@ -848,7 +850,7 @@ class MentoringWithExplicitStepsBlock(BaseMentoringBlock, StudioContainerWithNes
         enforce_type=True
     )
 
-    editable_fields = ('display_name', 'max_attempts', 'extended_feedback')
+    editable_fields = ('display_name', 'max_attempts', 'extended_feedback', 'weight')
 
     @lazy
     def question_ids(self):
@@ -864,6 +866,27 @@ def questions(self):
         """
         return [self.runtime.get_block(question_id) for question_id in self.question_ids]
 
+    @property
+    def active_step_safe(self):
+        """
+        Get self.active_step and double-check that it is a valid value.
+        The stored value could be invalid if this block has been edited and new steps were
+        added/deleted.
+        """
+        active_step = self.active_step
+        if active_step >= 0 and active_step < len(self.step_ids):
+            return active_step
+        if active_step == -1 and self.has_review_step:
+            return active_step  # -1 indicates the review step
+        return 0
+
+    def get_active_step(self):
+        """ Get the active step as an instantiated XBlock """
+        block = self.runtime.get_block(self.step_ids[self.active_step_safe])
+        if block is None:
+            log.error("Unable to load step builder step child %s", self.step_ids[self.active_step_safe])
+        return block
+
     @lazy
     def step_ids(self):
         """
@@ -956,6 +979,8 @@ def student_view(self, context):
         fragment = Fragment()
         children_contents = []
 
+        context = context or {}
+        context['hide_prev_answer'] = True  # For Step Builder, we don't show the users' old answers when they try again
         for child_id in self.children:
             child = self.runtime.get_block(child_id)
             if child is None:  # child should not be None but it can happen due to bugs or permission issues
@@ -1003,36 +1028,45 @@ def allowed_nested_blocks(self):
         ]
 
     @XBlock.json_handler
-    def update_active_step(self, new_value, suffix=''):
+    def submit(self, data, suffix=None):
+        """
+        Called when the user has submitted the answer[s] for the current step.
+        """
+        # First verify that active_step is correct:
+        if data.get("active_step") != self.active_step_safe:
+            raise JsonHandlerError(400, "Invalid Step. Refresh the page and try again.")
+
+        # The step child will process the data:
+        step_block = self.get_active_step()
+        if not step_block:
+            raise JsonHandlerError(500, "Unable to load the current step block.")
+        response_data = step_block.submit(data)
+
+        # Update the active step:
+        new_value = self.active_step_safe + 1
         if new_value < len(self.step_ids):
             self.active_step = new_value
         elif new_value == len(self.step_ids):
+            # The user just completed the final step.
             if self.has_review_step:
                 self.active_step = -1
-        return {
-            'active_step': self.active_step
-        }
-
-    @XBlock.json_handler
-    def update_num_attempts(self, data, suffix=''):
-        if self.num_attempts < self.max_attempts:
-            self.num_attempts += 1
-        return {
-            'num_attempts': self.num_attempts
-        }
+            # Update the number of attempts, if necessary:
+            if self.num_attempts < self.max_attempts:
+                self.num_attempts += 1
+            response_data['num_attempts'] = self.num_attempts
+            # And publish the score:
+            score = self.score
+            grade_data = {
+                'value': score.raw,
+                'max_value': self.max_score(),
+            }
+            self.runtime.publish(self, 'grade', grade_data)
+            response_data['grade_data'] = self.get_grade()
 
-    @XBlock.json_handler
-    def publish_attempt(self, data, suffix):
-        score = self.score
-        grade_data = {
-            'value': score.raw,
-            'max_value': 1,
-        }
-        self.runtime.publish(self, 'grade', grade_data)
-        return {}
+        response_data['active_step'] = self.active_step
+        return response_data
 
-    @XBlock.json_handler
-    def get_grade(self, data, suffix):
+    def get_grade(self, data=None, suffix=None):
         score = self.score
         return {
             'score': score.percentage,
diff --git a/problem_builder/mrq.py b/problem_builder/mrq.py
index d7461166..6e06e404 100644
--- a/problem_builder/mrq.py
+++ b/problem_builder/mrq.py
@@ -148,7 +148,7 @@ def calculate_results(self, submissions):
             'submissions': submissions,
             'status': status,
             'choices': results,
-            'message': self.message,
+            'message': self.message_formatted,
             'weight': self.weight,
             'score': (float(score) / len(results)) if results else 0,
         }
diff --git a/problem_builder/public/js/mentoring_with_steps.js b/problem_builder/public/js/mentoring_with_steps.js
index 443065af..1bc9c634 100644
--- a/problem_builder/public/js/mentoring_with_steps.js
+++ b/problem_builder/public/js/mentoring_with_steps.js
@@ -55,60 +55,22 @@ function MentoringWithStepsBlock(runtime, element) {
         } else {
             checkmark.addClass('checkmark-incorrect icon-exclamation fa-exclamation');
         }
-    }
-
-    function postUpdateStep(response) {
-        activeStep = response.active_step;
-        if (activeStep === -1) {
-            updateNumAttempts();
-        } else {
-            updateControls();
+        var step = steps[activeStep];
+        if (typeof step.showFeedback == 'function') {
+            step.showFeedback(response);
         }
     }
 
-    function handleResults(response) {
-        showFeedback(response);
-
-        // Update active step:
-        // If we end up at the review step, proceed with updating the number of attempts used.
-        // Otherwise, get UI ready for showing next step.
-        var handlerUrl = runtime.handlerUrl(element, 'update_active_step');
-        $.post(handlerUrl, JSON.stringify(activeStep+1))
-            .success(postUpdateStep);
-    }
-
-    function updateNumAttempts() {
-        var handlerUrl = runtime.handlerUrl(element, 'update_num_attempts');
-        $.post(handlerUrl, JSON.stringify({}))
-            .success(function(response) {
-                attemptsDOM.data('num_attempts', response.num_attempts);
-                publishAttempt();
-            });
-    }
-
-    function publishAttempt() {
-        var handlerUrl = runtime.handlerUrl(element, 'publish_attempt');
-        $.post(handlerUrl, JSON.stringify({}))
-            .success(function(response) {
-                // Now that relevant info is up-to-date and attempt has been published, get the latest grade
-                updateGrade();
-            });
-    }
-
-    function updateGrade() {
-        var handlerUrl = runtime.handlerUrl(element, 'get_grade');
-        $.post(handlerUrl, JSON.stringify({}))
-            .success(function(response) {
-                gradeDOM.data('score', response.score);
-                gradeDOM.data('correct_answer', response.correct_answers);
-                gradeDOM.data('incorrect_answer', response.incorrect_answers);
-                gradeDOM.data('partially_correct_answer', response.partially_correct_answers);
-                gradeDOM.data('correct', response.correct);
-                gradeDOM.data('incorrect', response.incorrect);
-                gradeDOM.data('partial', response.partial);
-                gradeDOM.data('assessment_review_tips', response.assessment_review_tips);
-                updateReviewStep(response);
-            });
+    function updateGrade(grade_data) {
+        gradeDOM.data('score', grade_data.score);
+        gradeDOM.data('correct_answer', grade_data.correct_answers);
+        gradeDOM.data('incorrect_answer', grade_data.incorrect_answers);
+        gradeDOM.data('partially_correct_answer', grade_data.partially_correct_answers);
+        gradeDOM.data('correct', grade_data.correct);
+        gradeDOM.data('incorrect', grade_data.incorrect);
+        gradeDOM.data('partial', grade_data.partial);
+        gradeDOM.data('assessment_review_tips', grade_data.assessment_review_tips);
+        updateReviewStep(grade_data);
     }
 
     function updateReviewStep(response) {
@@ -136,16 +98,27 @@ function MentoringWithStepsBlock(runtime, element) {
     }
 
     function submit() {
-        // We do not handle submissions at this level, so just forward to "submit" method of active step
-        var step = steps[activeStep];
-        step.submit(handleResults);
-    }
-
-    function markRead() {
-        var handlerUrl = runtime.handlerUrl(element, 'update_active_step');
-        $.post(handlerUrl, JSON.stringify(activeStep+1)).success(function (response) {
-            postUpdateStep(response);
-            updateDisplay();
+        submitDOM.attr('disabled', 'disabled'); // Disable the button until the results load.
+        var submitUrl = runtime.handlerUrl(element, 'submit');
+
+        var hasQuestion = steps[activeStep].hasQuestion();
+        var data = steps[activeStep].getSubmitData();
+        data["active_step"] = activeStep;
+        $.post(submitUrl, JSON.stringify(data)).success(function(response) {
+            showFeedback(response);
+            activeStep = response.active_step;
+            if (activeStep === -1) {
+                // We are now showing the review step / end
+                // Update the number of attempts.
+                attemptsDOM.data('num_attempts', response.num_attempts);
+                updateGrade(response.grade_data);
+            } else if (!hasQuestion) {
+                // This was a step with no questions, so proceed to the next step / review:
+                updateDisplay();
+            } else {
+                // Enable the Next button so users can proceed.
+                updateControls();
+            }
         });
     }
 
@@ -332,11 +305,11 @@ function MentoringWithStepsBlock(runtime, element) {
         if (isLastStep() && step.hasQuestion()) {
             nextDOM.hide();
         } else if (isLastStep()) {
-            reviewDOM.one('click', markRead);
+            reviewDOM.one('click', submit);
             reviewDOM.removeAttr('disabled');
             nextDOM.hide()
         } else if (!step.hasQuestion()) {
-            nextDOM.one('click', markRead);
+            nextDOM.one('click', submit);
         }
         if (step.hasQuestion()) {
             submitDOM.show();
diff --git a/problem_builder/public/js/questionnaire.js b/problem_builder/public/js/questionnaire.js
index 95592d78..4a4a8b27 100644
--- a/problem_builder/public/js/questionnaire.js
+++ b/problem_builder/public/js/questionnaire.js
@@ -122,7 +122,12 @@ function MCQBlock(runtime, element) {
             var mentoring = this.mentoring;
 
             var messageView = MessageView(element, mentoring);
-            messageView.clearResult();
+            
+            if (result.message) {
+                var msg = '<div class="message-content">' + result.message + '</div>' +
+                          '<div class="close icon-remove-sign fa-times-circle"></div>';
+                messageView.showMessage(msg);
+            } else { messageView.clearResult(); }
 
             display_message(result.message, messageView, options.checkmark);
 
diff --git a/problem_builder/public/js/step.js b/problem_builder/public/js/step.js
index 430a40dd..d2b74590 100644
--- a/problem_builder/public/js/step.js
+++ b/problem_builder/public/js/step.js
@@ -44,29 +44,25 @@ function MentoringStepBlock(runtime, element) {
             return is_valid;
         },
 
-        submit: function(resultHandler) {
-            var handler_name = 'submit';
+        getSubmitData: function() {
             var data = {};
             for (var i = 0; i < children.length; i++) {
                 var child = children[i];
                 if (child && child.name !== undefined) {
-                    data[child.name.toString()] = callIfExists(child, handler_name);
+                    data[child.name.toString()] = callIfExists(child, "submit");
                 }
             }
-            var handlerUrl = runtime.handlerUrl(element, handler_name);
-            if (submitXHR) {
-                submitXHR.abort();
-            }
-            submitXHR = $.post(handlerUrl, JSON.stringify(data))
-                .success(function(response) {
-                    resultHandler(response);
-                    if (message.length) {
-                        message.fadeIn();
-                        $(document).click(function() {
-                            message.fadeOut();
-                        });
-                    }
+            return data;
+        },
+
+        showFeedback: function(response) {
+            // Called when user has just submitted an answer or is reviewing their answer durign extended feedback.
+            if (message.length) {
+                message.fadeIn();
+                $(document).click(function() {
+                    message.fadeOut();
                 });
+            }
         },
 
         getResults: function(resultHandler) {
diff --git a/problem_builder/questionnaire.py b/problem_builder/questionnaire.py
index 301da80f..321483c5 100644
--- a/problem_builder/questionnaire.py
+++ b/problem_builder/questionnaire.py
@@ -221,3 +221,14 @@ def get_review_tip(self):
                 child = self.runtime.get_block(child_id)
                 if child.type == "on-assessment-review-question":
                     return child.content
+
+    @property
+    def message_formatted(self):
+        """ Get the feedback message HTML, if any, formatted by the runtime """
+        if self.message:
+            # For any HTML that we aren't 'rendering' through an XBlock view such as
+            # student_view the runtime may need to rewrite URLs
+            # e.g. converting '/static/x.png' to '/c4x/.../x.png'
+            format_html = getattr(self.runtime, 'replace_urls', lambda html: html)
+            return format_html(self.message)
+        return ""
diff --git a/problem_builder/step.py b/problem_builder/step.py
index dbd6a01b..7cac2f59 100644
--- a/problem_builder/step.py
+++ b/problem_builder/step.py
@@ -160,8 +160,8 @@ def allowed_nested_blocks(self):
     def has_question(self):
         return any(getattr(child, 'answerable', False) for child in self.steps)
 
-    @XBlock.json_handler
-    def submit(self, submissions, suffix=''):
+    def submit(self, submissions):
+        """ Handle a student submission. This is called by the parent XBlock. """
         log.info(u'Received submissions: {}'.format(submissions))
 
         # Submit child blocks (questions) and gather results
@@ -177,6 +177,7 @@ def submit(self, submissions, suffix=''):
         self.reset()
         for result in submit_results:
             self.student_results.append(result)
+        self.save()
 
         return {
             'message': 'Success!',
diff --git a/problem_builder/templates/html/mcqblock.html b/problem_builder/templates/html/mcqblock.html
index 95443bf5..14da13c0 100644
--- a/problem_builder/templates/html/mcqblock.html
+++ b/problem_builder/templates/html/mcqblock.html
@@ -10,7 +10,7 @@
       <div class="choice-selector">
         <input id="choice-{{ self.html_id }}-{{ forloop.counter }}" type="radio"
           name="{{ self.name }}" value="{{ choice.value }}"
-          {% if self.student_choice == choice.value %} checked{% endif %}
+          {% if self.student_choice == choice.value and not hide_prev_answer %} checked{% endif %}
         />
       </div>
       <label class="choice-label" for="choice-{{ self.html_id }}-{{ forloop.counter }}">
diff --git a/problem_builder/templates/html/mentoring_with_steps.html b/problem_builder/templates/html/mentoring_with_steps.html
index 0839a523..41d861f9 100644
--- a/problem_builder/templates/html/mentoring_with_steps.html
+++ b/problem_builder/templates/html/mentoring_with_steps.html
@@ -1,5 +1,5 @@
 {% load i18n %}
-<div class="mentoring themed-xblock" data-active-step="{{ self.active_step }}">
+<div class="mentoring themed-xblock" data-active-step="{{ self.active_step_safe }}">
 
   {% if show_title and title %}
   <div class="title">
diff --git a/problem_builder/templates/html/mrqblock.html b/problem_builder/templates/html/mrqblock.html
index a3679195..b7760367 100644
--- a/problem_builder/templates/html/mrqblock.html
+++ b/problem_builder/templates/html/mrqblock.html
@@ -10,7 +10,7 @@
       <div class="choice-selector">
         <input id="choice-{{ self.html_id }}-{{ forloop.counter }}" type="checkbox"
          name="{{ self.name }}" value="{{ choice.value }}"
-         {% if choice.value in self.student_choices %} checked{% endif %}
+         {% if choice.value in self.student_choices and not hide_prev_answer %} checked{% endif %}
         />
       </div>
       <label class="choice-label" for="choice-{{ self.html_id }}-{{ forloop.counter }}">
diff --git a/problem_builder/templates/html/ratingblock.html b/problem_builder/templates/html/ratingblock.html
index 90d04d7b..45a5178e 100644
--- a/problem_builder/templates/html/ratingblock.html
+++ b/problem_builder/templates/html/ratingblock.html
@@ -10,7 +10,7 @@
         <div class="choice-selector">
           <input id="choice-{{ self.html_id }}-{{i}}" type="radio"
             name="{{ self.name }}" value="{{i}}"
-            {% if self.student_choice == i %} checked{%else%} data-student-choice='{{self.student_choice}}'{% endif %}
+            {% if self.student_choice == i and not hide_prev_answer %} checked{%else%} data-student-choice='{{self.student_choice}}'{% endif %}
             />
         </div>
         <label class="choice-label" for="choice-{{ self.html_id }}-{{i}}">
@@ -30,7 +30,7 @@
       <div class="choice-selector">
         <input id="choice-{{ self.html_id }}-custom{{ forloop.counter }}" type="radio"
           name="{{ self.name }}" value="{{ choice.value }}"
-          {% if self.student_choice == choice.value %} checked{%else%} data-student-choice='{{self.student_choice}}'{% endif %}
+          {% if self.student_choice == choice.value and not hide_prev_answer %} checked{%else%} data-student-choice='{{self.student_choice}}'{% endif %}
         />
       </div>
       <label class="choice-label" for="choice-{{ self.html_id }}-custom{{ forloop.counter }}">
diff --git a/problem_builder/templates/xml/mentoring_demo.xml b/problem_builder/templates/xml/mentoring_demo.xml
index df33f0a8..6401fedf 100644
--- a/problem_builder/templates/xml/mentoring_demo.xml
+++ b/problem_builder/templates/xml/mentoring_demo.xml
@@ -22,7 +22,7 @@
             <p>And here is an example of a Multiple Choice Question (MCQ):</p>
         </html_demo>
 
-        <pb-mcq name="plain_mcq" question="Which book includes the line &quot;But I have one want which I have never yet been able to satisfy, and the absence of the object of which I now feel as a most severe evil. I have no friend.&quot;?" correct_choices="frankenstein">
+        <pb-mcq name="plain_mcq" question="Which book includes the line &quot;But I have one want which I have never yet been able to satisfy, and the absence of the object of which I now feel as a most severe evil. I have no friend.&quot;?" correct_choices='["frankenstein"]'>
             <pb-choice value="frankenstein"><em>Frankenstein</em></pb-choice>
             <pb-choice value="moby"><em>Moby-Dick; or, The Whale</em></pb-choice>
             <pb-choice value="twist"><em>Oliver Twist</em></pb-choice>
@@ -40,19 +40,19 @@
             <p>How did you like <em>To Kill a Mockingbird</em>?</p>
         </html_demo>
 
-        <pb-rating name="rate_mockingbird" low="I really disliked it" high="I loved it" correct_choices="1,2,3,4,5" />
+        <pb-rating name="rate_mockingbird" low="I really disliked it" high="I loved it" correct_choices='["1","2","3","4","5"]' />
     </problem-builder>
 
     <problem-builder display_name="Multiple Response Question (and introducing tips)" weight="1" mode="standard">
         <html_demo><p>A fourth type of question is the Multiple Response Question (MRQ), which allows student to select multiple answers. Each answer can be marked as required, not required, or acceptable either way. The following question contains examples of each possibility. Try getting it wrong and see how it provides feedback to guide you to a correct answer.</p></html_demo>
-        <pb-mrq name="future_movies" question="Which of these films are set in the future?" required_choices="apes" ignored_choices="2001">
+        <pb-mrq name="future_movies" question="Which of these films are set in the future?" required_choices='["apes"]' ignored_choices='["2001"]'>
             <pb-choice value="starwars">Star Wars Episode V: The Empire Strikes Back</pb-choice>
             <pb-choice value="2001">2001: A Space Odyssey</pb-choice>
             <pb-choice value="apes">Planet of the Apes (1968)</pb-choice>
 
-            <pb-tip values="starwars">Star Wars takes place "A long time ago in a galaxy far, far away"</pb-tip>
-            <pb-tip values="2001">You could argue this one either way. When the film was released in 1968, it was set in the future. However, 2001 is now in the past.</pb-tip>
-            <pb-tip values="apes">The majority of the film takes place in the year 3978.</pb-tip>
+            <pb-tip values='["starwars"]'>Star Wars takes place "A long time ago in a galaxy far, far away"</pb-tip>
+            <pb-tip values='["2001"]'>You could argue this one either way. When the film was released in 1968, it was set in the future. However, 2001 is now in the past.</pb-tip>
+            <pb-tip values='["apes"]'>The majority of the film takes place in the year 3978.</pb-tip>
         </pb-mrq>
 
         <pb-message type="incomplete">
@@ -69,14 +69,14 @@
             <p>Like the MRQ above, multiple choice and rating questions can also provide feedback based on which answer was selected and whether the answer is correct or not. Here's an example:</p>
         </html_demo>
 
-        <pb-mcq name="subjunctive" question="Which sentence correctly uses the subjunctive case?" correct_choices="d">
+        <pb-mcq name="subjunctive" question="Which sentence correctly uses the subjunctive case?" correct_choices='["d"]'>
             <pb-choice value="a">To buy or not to buy, that is the question.</pb-choice>
             <pb-choice value="b">Renting gives you more flexibility.</pb-choice>
             <pb-choice value="c">If I was you, I'd buy the house.</pb-choice>
             <pb-choice value="d">If I were you, I'd rent the house.</pb-choice>
-            <pb-tip values="a,b">This sentence is not discussing hypotheticals or impossibilities.</pb-tip>
-            <pb-tip values="c">This sentence should be using the subjunctive case since it's dicsussing a hypothetical, but "was" is the wrong case.</pb-tip>
-            <pb-tip values="d">Correct. "was" has become "were" to indicate the subjunctive case.</pb-tip>
+            <pb-tip values='["a","b"]'>This sentence is not discussing hypotheticals or impossibilities.</pb-tip>
+            <pb-tip values='["c"]'>This sentence should be using the subjunctive case since it's dicsussing a hypothetical, but "was" is the wrong case.</pb-tip>
+            <pb-tip values='["d"]'>Correct. "was" has become "were" to indicate the subjunctive case.</pb-tip>
         </pb-mcq>
 
         <pb-message type="incomplete">
@@ -111,20 +111,20 @@
     </problem-builder>
     <problem-builder display_name="Assessment Example" mode="assessment">
         <html_demo><p>Mentoring questions can also be asked in "Assessment" mode, where each question is asked one at a time, and a final score is shown at the end. The author can set how many attempts each student is given to go through the assessment.</p></html_demo>
-        <pb-mcq name="aq1" question="What is 7+3?" correct_choices="ten">
+        <pb-mcq name="aq1" question="What is 7+3?" correct_choices='["ten"]'>
             <pb-choice value="ten">10</pb-choice>
             <pb-choice value="prime">104,297</pb-choice>
             <pb-choice value="infinity">Infinity</pb-choice>
             <pb-choice value="undefined">Undefined</pb-choice>
         </pb-mcq>
-        <pb-mcq name="aq2" question="What is the square root of nine?" correct_choices="three">
+        <pb-mcq name="aq2" question="What is the square root of nine?" correct_choices='["three"]'>
             <pb-choice value="zero">1</pb-choice>
             <pb-choice value="three">3</pb-choice>
             <pb-choice value="nine">9</pb-choice>
             <pb-choice value="infinity">Infinity</pb-choice>
             <pb-choice value="undefined">Undefined</pb-choice>
         </pb-mcq>
-        <pb-mcq name="aq3" question="What is 10&#247;0?" correct_choices="infinity,undefined">
+        <pb-mcq name="aq3" question="What is 10&#247;0?" correct_choices='["infinity","undefined"]'>
             <pb-choice value="zero">0</pb-choice>
             <pb-choice value="ten">10</pb-choice>
             <pb-choice value="negten">-10</pb-choice>
diff --git a/problem_builder/templates/xml/mentoring_with_only_one_step.xml b/problem_builder/templates/xml/mentoring_with_only_one_step.xml
index d9abdc33..45a52d8c 100644
--- a/problem_builder/templates/xml/mentoring_with_only_one_step.xml
+++ b/problem_builder/templates/xml/mentoring_with_only_one_step.xml
@@ -3,15 +3,15 @@
         <p>Please answer the questions below.</p>
     </html_demo>
 
-    <pb-mrq name="mrq_1_1" question="What do you like in this MRQ?" message="Thank you for answering!" required_choices="gracefulness,elegance,beauty">
+    <pb-mrq name="mrq_1_1" question="What do you like in this MRQ?" message="Thank you for answering!" required_choices='["gracefulness","elegance","beauty"]'>
         <pb-choice value="elegance">Its elegance</pb-choice>
         <pb-choice value="beauty">Its beauty</pb-choice>
         <pb-choice value="gracefulness">Its gracefulness</pb-choice>
         <pb-choice value="bugs">Its bugs</pb-choice>
 
-        <pb-tip values="gracefulness">This MRQ is indeed very graceful</pb-tip>
-        <pb-tip values="elegance,beauty">This is something everyone has to like about this MRQ</pb-tip>
-        <pb-tip values="bugs">Nah, there aren't any!</pb-tip>
+        <pb-tip values='["gracefulness"]'>This MRQ is indeed very graceful</pb-tip>
+        <pb-tip values='["elegance","beauty"]'>This is something everyone has to like about this MRQ</pb-tip>
+        <pb-tip values='["bugs"]'>Nah, there aren't any!</pb-tip>
     </pb-mrq>
 
     <pb-message type="completed">
diff --git a/problem_builder/tests/integration/test_step_builder.py b/problem_builder/tests/integration/test_step_builder.py
index 116e5db5..2ad70d7e 100644
--- a/problem_builder/tests/integration/test_step_builder.py
+++ b/problem_builder/tests/integration/test_step_builder.py
@@ -100,6 +100,16 @@ def setUp(self):
         runtime_patcher.start()
         self.addCleanup(runtime_patcher.stop)
 
+        # Mock replace_urls so that we can check that message HTML gets processed with any
+        # transforms that the runtime needs.
+        runtime_patcher2 = patch(
+            'workbench.runtime.WorkbenchRuntime.replace_urls',
+            lambda _runtime, html: html.replace('REPLACE-ME', ''),
+            create=True
+        )
+        runtime_patcher2.start()
+        self.addCleanup(runtime_patcher2.stop)
+
     def freeform_answer(
             self, number, step_builder, controls, text_input, result, saved_value="", hold=False, last=False
     ):
@@ -425,6 +435,9 @@ def test_step_builder(self, params):
             None, step_builder, controls, 'This is a different answer', CORRECT, saved_value='This is the answer'
         )
         # Step 2
+        # Reload the page, which should have no effect
+        self.browser.execute_script("$(document).html(' ');")
+        step_builder, controls = self.go_to_assessment()
         # Submit MCQ, go to next step
         self.single_choice_question(None, step_builder, controls, 'Yes', CORRECT)
         # Step 3
diff --git a/problem_builder/tests/integration/xml_templates/step_builder.xml b/problem_builder/tests/integration/xml_templates/step_builder.xml
index a60ba87c..0007f3d3 100644
--- a/problem_builder/tests/integration/xml_templates/step_builder.xml
+++ b/problem_builder/tests/integration/xml_templates/step_builder.xml
@@ -41,7 +41,7 @@
     </sb-step>
 
   <sb-step display_name="Last step">
-    <pb-mrq name="mrq_1_1" question="What do you like in this MRQ?" required_choices='["gracefulness","elegance","beauty"]' message="Question Feedback Message">
+    <pb-mrq name="mrq_1_1" question="What do you like in this MRQ?" required_choices='["gracefulness","elegance","beauty"]' message="Question Feedback Message REPLACE-ME">
       <pb-choice value="elegance">Its elegance</pb-choice>
       <pb-choice value="beauty">Its beauty</pb-choice>
       <pb-choice value="gracefulness">Its gracefulness</pb-choice>
diff --git a/problem_builder/tests/unit/test_common.py b/problem_builder/tests/unit/test_common.py
new file mode 100644
index 00000000..067e9523
--- /dev/null
+++ b/problem_builder/tests/unit/test_common.py
@@ -0,0 +1,26 @@
+"""
+Tests common to Problem Builder and Step Builder
+"""
+import ddt
+import unittest
+from problem_builder.mentoring import MentoringBlock, MentoringWithExplicitStepsBlock
+from xblock.core import XBlock
+
+from .utils import ScoresTestMixin, instantiate_block
+
+
+@ddt.ddt
+class TestBuilderBlocks(ScoresTestMixin, unittest.TestCase):
+    """ Unit tests for Problem Builder and Step Builder """
+
+    @ddt.data(MentoringBlock, MentoringWithExplicitStepsBlock)
+    def test_interface(self, block_cls):
+        """
+        Basic tests of the block's public interface.
+        """
+        self.assertTrue(issubclass(block_cls, XBlock))
+        self.assertTrue(block_cls.has_children)
+
+        block = instantiate_block(block_cls)
+        self.assertTrue(block.has_children)
+        self.assert_produces_scores(block)
diff --git a/problem_builder/tests/unit/test_mentoring.py b/problem_builder/tests/unit/test_problem_builder.py
similarity index 100%
rename from problem_builder/tests/unit/test_mentoring.py
rename to problem_builder/tests/unit/test_problem_builder.py
diff --git a/problem_builder/tests/unit/utils.py b/problem_builder/tests/unit/utils.py
new file mode 100644
index 00000000..48652a57
--- /dev/null
+++ b/problem_builder/tests/unit/utils.py
@@ -0,0 +1,37 @@
+"""
+Helper methods for testing Problem Builder / Step Builder blocks
+"""
+from mock import MagicMock, Mock
+from xblock.field_data import DictFieldData
+
+
+class ScoresTestMixin(object):
+    """
+    Mixin for tests that involve scores (grades)
+    """
+    def assert_produces_scores(self, block):
+        """
+        Test that the given XBlock instance meets the requirements of being able to report
+        scores to the edX LMS, and have them appear on the student's progress page.
+        """
+        self.assertTrue(block.has_score)
+        self.assertTrue(type(block).has_score)
+        self.assertEqual(block.weight, 1.0)  # Default weight should be 1
+        self.assertIsInstance(block.max_score(), (int, float))
+
+
+def instantiate_block(cls, fields=None):
+    """
+    Instantiate the given XBlock in a mock runtime.
+    """
+    fields = fields or {}
+    children = fields.pop('children', {})
+    field_data = DictFieldData(fields or {})
+    block = cls(
+        runtime=Mock(),
+        field_data=field_data,
+        scope_ids=MagicMock()
+    )
+    block.children = children
+    block.runtime.get_block = lambda child_id: children[child_id]
+    return block