This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. A member of the same class at school.

n. Someone who is in the same class (in school)

n. One who is in the same class with another, as at school or college.

n. One of the same class at school or college; a class-fellow.

n. an acquaintance that you go to school with

"One day he called a classmate, whom he was tormenting, a Jew."

acquaintance    friend   

schoolmate   

chum    mentor    schoolmate    dropout    roommate    shipmate    co-worker    crony    playmate    counselor