also: おなクラ
noun
Colloquial abbreviation of 同じクラス, used mainly among students to refer to being in the same class. The reading おなクラ is more casual and slangy; どうクラ is the straightforward on-reading abbreviation.
あの子、おなクラなんだって。
I heard that kid is in the same class as us.
どうクラの友達と一緒に帰った。
I went home with a friend from the same class.
The full, standard phrase; 同クラ is a casual abbreviation used in informal conversation.
Abbreviation of 同じクラス (same class). The reading おなクラ is a contraction of おなじ + クラス, while どうクラ uses the on-reading of 同.