Abstract This chapter examines some effects of California’s Class Size Reduction (CSR) policy on teachers and pupils in four elementary schools over a two year period using interviews and participant observation. Among the main findings from the interviews, confirmed by the observations, was that while teachers found classes with 20 pupils easier to teach, they did not initially consider the possibility of changing practice in order to maximize the advantages of the smaller classes. In the second year there were slight increases in the amounts of individual attention pupils received, particularly feedback, and teachers expressed greater confidence when making assessments. Pupils’ reactions were generally positive although some expressed the view that in larger classes they got more help from friends. There were several unanticipated effects; for example, some older grade teachers with larger classes expressed resentment because of their higher administrative and marking loads.