The aim of this study was to develop and validate a psychometrically-sound instrument to assess students' perceptions about class cohesion. Two studies were conducted. In Study 1, four steps were established: (1) development of the Class Cohesion Questionnaire (CCQ); (2) item selection; (3) item compression; and (4) exploration of psychometric properties. In Study 2, participants were 1504 students from 21 primary and secondary schools. The aim was to confirm the psychometric properties and to create a short version of the instrument (CCQ-SF). In Study 1, the CCQ showed adequate content and construct validity, with a factorial structure of two first-order factors (task cohesion and social cohesion), and adequate internal consistency. In Study 2, the CCQ and CCQ-SF confirmed adequate factorial structure and reliability, discriminant and nomological validity, and showed invariance by sex and educational stage. The CCQ and the CCQ-SF are valid and reliable instruments to measure class cohesion in educational settings.