Previous work on policy implementation has often suggested that schools leave their "thumbprints" on policies received from above. During the implementation of Primary Class Size Reduction (PCS) Initiative in Ontario, Canada, however, school principals spoke with remarkable uniformity about the ways PCS affected their work. This article reports the interview responses of 24 principals from eight school districts across Ontario that participated in a larger multiyear evaluation of PCS. The article analyzes principals' perspectives on the constraints of middle management under this policy and also raises questions about how policy shapes principals' leadership discretion and influence on crucial school functions of teaching and learning.