Why can't this be "en elev" ?
It can be. Afaik, in Commonwealth English, "en elev" is a pupil and "en studerende" is a student, but in American English, we don't differentiate the two.
Reported: "en elev giver hende et rødt æble" should be accepted.
Also reported, better chance of an elementary school student bringing an apple that someone at a university.