This research is conducted in the context of a large-scale study of three nationally disseminated comprehensive school reform projects (CSRs) and examines how school- and classroom-level factors contribute to variation in instructional time in English language arts and mathematics. When using mean-based OLS regression techniques such as Hierarchical Linear Models (HLM), we found that CSR programs did not have the expected effects on instructional time. However, when using Quantile Regression to estimate the effects at the lower end of the distribution of instructional time, we found substantial effects. These effects were strongest for the subjects that were the focus of the school interventions. (Contains 2 figures and 2 tables.)