Bob is three years below me at school. Jane is two years ahead of me at school. Below or ahead are the most natural and common ways to say this. you can also say above you for being one year only. behind = implies that the person is mentally or academically less talented than you (behind) teachers tend to write reports saying "Donald is behind with his school work" "He is behind the other students and I feel he won't catch up".

Bob is three years ahead of me in school.

I think you could also technically say that someone is 'a year above you'. This one would be a bit more informal, I think.