Scaffolded proofs in a Moodle quiz

In my online course Fundamentals of Algebra and Calculus, there were several places where I wanted to encourage students to engage with a key proof while reading the text.

One approach to this is to ask proof comprehension questions after giving the proof, but I’ve also tried writing some sequences of questions that lead the students through the proof in a scaffolded/structured way.

Here’s a simple example, of a sketch proof of the Fundamental Theorem of Calculus:Screenshot of question showing a sketch and asking students to complete an expression for a shaded area in the sketch

Students can’t see the next part of the proof until they give an answer. Once they have submitted their answer, the next part is revealed:Solution to the task, followed by the rest of the proof

I’ve used this approach in other places in the course, sometimes with more than one step.

The way to do this in Moodle is by having the quiz settings set to “Interactive with multiple tries”:Then using the little padlock symbols that appear at the right-hand side between questions on the “Edit questions” page:

After clicking the padlock, it changes to locked to indicate that students must answer the first question to see the second:

I’ve not done any serious evaluation of this approach, but my intuition is that it’s a good way to direct students’ attention to certain parts of a proof and encourage them to be more active in their reading.

Moodle gradebook setup for mastery grading

In my course Fundamentals of Algebra and Calculus, students complete weekly Unit Tests. Their grade is determined by the number of Unit Tests passed at Mastery (80%+) or Distinction (95%+) levels. For instance, to pass the course, students need to get Mastery in at least 7 of the 10 units. You can find more details about the course in this paper:

  • Kinnear, G., Wood, A. K., Gratwick, R. (2021). Designing and evaluating an online course to support transition to university mathematicsInternational Journal of Mathematical Education in Science and Technology

All the Unit Tests are set up as Moodle quizzes, and I needed a way to compute the number of tests completed as Mastery level (and at Distinction level) for each student.

To make matters more complicated, there are 4 different versions of each Unit Test:

  • Unit Test – the first attempt
  • Unit Test Resit – a second attempt, available to students shortly after the first attempt if they did not reach Mastery
  • Unit Test (Extra Resit) – a third attempt, available at the end of semester
  • Unit Test (Resit Diet) – a fourth attempt, available during the resit diet in August

Each subsequent attempt replaces the result of previous ones – e.g. if a student with a Mastery result on the first attempt decides to take the Unit Test (Extra Resit) to try to get a Distinction, then they will lose the Mastery result if they do not reach the 80% threshold.

To set this up in the Moodle gradebook, I have given each of the variants an ID, with the pattern:

  • WnFT
  • WnFTR
  • WnFTR2
  • WnFTRD

(where n is the week number).

Then I have added a calculated grade item called “Number of Mastery results”, with a complicated formula to determine this. It is the sum of 10 terms like this:


where this snippet computes the number of Mastery results in week 1 (i.e. it will return 0 or 1).

Note that the 25.5 appears throughout this expression because that is the threshold for 80% on these tests.

  • ceil([[W1FTRD]]/32)*floor([[W1FTRD]]/25.5) means “if they took the Resit Diet version, then use their score on that to decide if they got a Mastery result”
  • (1-ceil([[W1FTRD]]/32))*(...) means “if they didn’t take the Resit Diet version, then use their other scores to decide”
  • There’s then a similar pattern with W1FTR2
  • And finally, if students didn’t take either W1FTRD or W1FTR2, we use the best of the W1FT and W1FTR results to decide (simple “best of” is OK here, since students can only take W1FTR if they did not get Mastery on W1FT).

This is all quite complicated, I know! It has grown up over time, as the FTR2 and FTRD versions were added after I first set up this approach.

Also, when I first implemented this, our version of Moodle did not support “if” statements – since the Moodle grade calculations can now make use of “if” statements, this calculation could be greatly simplified.

STACK: Checking answers in polar form

Last week’s topic in FAC was complex numbers, and I’ve had some difficulties with STACK questions asking students to give their answer in polar form, e.g. when the correct answer was 4*(cos(pi/3)+i*sin(pi/3)) an answer of 4*(cos((1/3)*pi)+i*sin((1/3)*pi)) would be marked incorrect!

The issue was that:

  • with simplification turned on, Maxima will automatically simplify polar form to cartesian form, so I need simplification off.
  • with simplification off, Maxima won’t see those equally valid ways of writing the argument as the same.

I was using the EqualComAss answer test to check whether the student answer (ans1) was equal to the model answer (ta1), and this was failing in the cases above.

The solution I came up with is to add some code to the feedback variables box at the top of the PRT, to replace cos and sin with alternate versions so that Maxima can’t simplify the expressions to cartesian form. I can then use ev(…,simp) to make use of simplification when comparing the expressions:

form_ans1:subst([cos=COSINE, sin=SINE], ans1);
form_ta1:subst([cos=COSINE, sin=SINE], ta1);

This will ensure that COSINE(pi/3) and COSINE((1/3)*pi) will cancel out, thanks to the simplification being turned on.

But since Maxima doesn’t know anything about COSINE, it can’t cancel out COSINE(-pi/3) and COSINE(5pi/3) (as it would do with cos) if students give their answer with the wrong value for the principal argument.

It was then just a case of replacing the test for EqualComAss(ans1,ta1) in the PRT with a test that AlgEquiv(proper_form, true), and regrading. Out of ~160 attempts this picked up 8 students who deserved full marks!

Update (08/11/2021): One year on, and STACK now has a new feature which makes it easier to grade these answers correctly! The new EqualComAssRules answer test lets you add a list of different algebraic rules so that two answers should count as equivalent if they differ only by those rules – e.g. x and 1*x.

To fix this question, it’s enough to change the first PRT node to the following, using the “Test options” box to specify the list of algebraic rules: