Asking practitioners to make larger changes to their practice is often thought to lead to lower fidelity of implementation. However, salient differences between ambitious new reforms and teachers' existing practices may also facilitate processes of conceptual change and correspondingly increase fidelity of implementation. I use survey data on the implementation of two Comprehensive School Reform programs to investigate this puzzle, presenting a series of descriptive multivariate regressions that--contrary to conventional wisdom--predominantly support a positive association between larger changes and higher fidelity. I also address alternative explanations for this finding and discuss the conceptual and empirical strengths and weaknesses, implications for future research, and potential utility for practice of each interpretation.