Preparing an exam is a task that is more difficult than it looks. The questions should not be too difficult nor too easy. The teacher must allow sufficient time but not too much. The teacher must also ensure that the questions are correctly interpreted. It is sometimes surprising to find that some students did not interpret the question as the teacher would have liked, but that the students were not entirely wrong in their interpretation either.
Having a question in which there is an error is always a problem. If the error is caught and identified during the exam, students who have already answered the original question will be confused. If the error is detected after the exam, the students may have answered differently according to their interpretation of the question and the correction becomes difficult. Either way, the situation is a bit chaotic.
There may be a problem when editing a Matching, Calculated or Formulas question after the quiz has been attempted. It is not that surprising. Some changes can be made, for example to the wording of the question or to the value of the variables, but as soon as variables are removed or added, it is very likely that Moodle will complain.
It would be possible to develop algorithms that would allow regrading a quiz whose variables had been changed, but that would be a difficult task both for the programming and for the exact way of doing it. I do not believe it is worth it and that it will happen in the near future.
The solution is rather not to make mistakes in preparing the exam questions. It seems a little strange to say this, but it is what it is. Here are a few things to consider:
- It is computer science. Everything must be well debugged, otherwise it doesn't work.
- With computer quizzes, which are corrected automatically, all of the teacher's work is done before the exam. The time saved by not having to mark the exams should be used by the teacher to properly prepare and debug the questions.
- The more questions the teacher prepares, the better he/she becomes at doing it, reducing preparation time and the risk of making mistakes.
- An exam question in which there is an error may need to be canceled. Too bad. However, when the question is debugged, it can be used in the next terms.
Other teachers are looking for ready-made questions. They are not wrong since they devote their time to other activities. But these questions, perhaps on other commercial LMS's, are, more often than not, straightforward true or false and multiple choice questions. Of course, they will have been debugged by the publisher and will not have to be regraded.
Personally, I much prefer the Moodle LMS. I only regret that there are not more ready-made questions grouped by subject or for example questions that would go with a book. But it will come one day.