Few evidence-based instructional practices achieve large-scale use, often remaining only in the schools directly involved in their development. Research on scaling up effective educational practice often lacks sensitive measures of the practice's implementation and the required research protocol. This article describes how we used rate of implementation as a sensitive measure to help identify barriers to implementation of class-wide peer tutoring (CWPT). Using communication technologies and a learning management system, we monitored the rate of CWPT implementation and its research protocol across nine schools in five states. Rate of implementation was defined as the number of weeks in which a school successfully completed the 12 implementation tasks required to reach full implementation. We discuss factors related to the variation in implementation rate (30-50 weeks) between schools, and implications of this measurement strategy for research on instructional practices and the technology used to facilitate scalability research.