同級 (dōkyū) means “same grade” | MotiTan Japanese Dictionary

More examples

私は同級の友達に宿題を見せてもらいました。watashi wa dō kyū no tomo dachi ni shuku dai o mi se te mo ra i ma shi ta

I had a friend in the same grade show me the homework.

Describes people or things that share the same level, especially the same school year.

同学年dōgakunen: People or things that belong to the same school year.
同期dōki: People who entered a school or organization in the same year.

学校などで、同じ学年や等級に属すること。gak kō na do de ona ji gaku nen ya tō kyū ni zoku su ru ko to

A Sino-Japanese compound, 同級 (dōkyū) combines 同 (dō, "same") and 級 (kyū, "grade" or "rank"), giving the sense of the same level.

In Japanese school terms, a grade means a whole school year, so this word usually signals the same year rather than the same homeroom.