There was substantial flexibility in how teachers could implement the approach, and as a result the fidelity of implementation varied across teachers. There were varia-tions across teachers in how much time they spent on the approach during class, how classroom activities were structured, and how they assessed student understanding of the approach. Despite these differences, there were some common elements across all of the schools. Each teacher devoted at least two class periods to the approach for each 2–3 week long topic unit studied. They were all accustomed to having students work together in cooperative groups of between two and four students during class, and CPS was no exception to this procedure. All of the teachers chose to grade students on their use of the approach in some fashion, and typically this occurred on an exam. How teachers implemented the approach was in fact one of the factors of interest and so we report below on our observations regarding implementation as well as teachers' descriptions of their own implementation of the CPS approach.