The Collaborative International Dictionary of English v.0.48:

Schoolmate \School"mate`\, n.
   A pupil who attends the same school as another.
   [1913 Webster]

WordNet (r) 3.0 (2006):

schoolmate
    n 1: an acquaintance that you go to school with [syn:
         schoolmate, classmate, schoolfellow, class fellow]