If you do not care about the score itself, but do care about who is the best in class, you should use ranker + binary classes as a target. Create a column "Is_first", and set it to 1 for the best students in each class and to 0 for the rest, then fit the ranker (not a classifier). In this case the result is going to be be a value between 1 and 0. Not sure it will sum up to 1 for all the students in class (you can write some code to normalize values if they do not sum up to 1).