[tóng xué]
(在同一学校[班级]学习) be in the same school [class]; be a schoolmate of sb.
I studied in the same school with them for three years.
我和他们同过3年学。
(在一起学习的人) fellow student; schoolmate; classmate
(称呼学生) comrade (a form of address used in speaking to a student)