Grades min max
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Summary
If a grade item of has its max points changed after someone receives a grade, then the resulting computed grade becomes very different from previous version of Moodle. Steps to reproduce
You can recreate the problem in 2.8 without the upgrade step. You will need a course with two users, A and B.
- Go into your gradebook and create a new manual Grade Item, leave it at the default 100 points and change the display to 'Real (Percent)'
- Give User A a grade of '10' and save.
- You should see the user has a grade of '10 (10%)'.
- Edit the grade item and set the maximum points to 10.
- Go back to the gradebook and give User B a grade of 10 and save.
- You will now see that User A has a grade of '10 (10%)' while User B has a grade of '10 (100%)'
- If you did this under 2.7, both users would have '10 (100%)', but then when you upgrade the site to 2.8, the grades would change to how you see them in the above example.
Background/Cause
When a grade is entered for a user, it is recorded in the grade_grade table. We record various bits of data, include the then current maxgrade of the grade_item, but under rawgrademax. In versions of Moodle prior to 2.8, when making derivative computations off the grade, we would always fetch grade_item->maxgrade, which contains the now max grade for the grade_item, and use that as the number of available points.
After the gradebook changes, grade_grade->rawgrademax is now used for the computation, in large part to support the computation of grades for different users with different sets of hidden grades. This has lead to a number of side effects:
- Percentages and any downstream computed grades (and number of points available) have changed for grade entries that have this problem.
- Two users with the same number of points for an item can see different percentages.
- Drop lowest/keep highest selections are wrong.
- If you have the Range rows on in the gradebook, it will show the 'expanded' range. So in our above example it will show 0-100, even though 10 is the max points.
- In the user report the user will see the expanded range.
How do users cause it
The most common thing we see is that teachers create a grade item for something, and forget to change the max points to what they want (usually 4 points). They then go and grade people. Then they see the mistake and change the max grade to be 4, with their intent (and the previous behavior being) that a user with a grade of 4 points has a 100%.
