Which supervised ML model to use for exam/grade prediction?
First you need to figure out what type of variable the response is. Is it categorical (eg. A, B, C, etc) or continuous (75%, 83%, 92%, etc)? If it's categorical, it'll definitely be ordinal. This means you can explore methods like ordered logistic regression. If it's continuous, look at something like beta regression.
For the app - if the student only keys in 3 of the 5 mock exam results, you could just get them to 'guess' their results for the other 2 mock exams. In my opinion, this is better than inputing the remaining 2 mock exam outcomes. This is since the student should have a good handle on they're going to perform.