1) Academic fellow 2) Acquaintance 3) Class fellow 4) Fellow freshman 5) Fellow student 6) Friend 7) Lab partner 8) Peer 9) School chum 10) School friend 11) Schoolfellow 12) Schoolmate 13) With whom one shares history 14) Yearbook signer 15) Yearbook signer, often 1) Fellowpupil 2) Peer 3) Schoolfellow 4) Schoolmate 
• (n.) One who is in the same class with another, as at school or college.
Class'mate` noun One who is in the same class with another, as at school or college. 
a member of the same class at a school or college.