Data regarding intervention utilization among the target population are critical to interpret evidence from efficacy trials for school-based interventions. When use of the intervention is voluntary, intervention diffusion becomes a particularly critical variable. We examined the use of Instructional Consultation Teams (IC Teams), a voluntary teacher support program designed to enhance teacher skills for working with students in the general education classroom. Teachers' use of IC Teams was measured in 17 schools implementing the program over 4 years. The percentage of teachers who used the team increased over time, but utilization rates differed substantially among schools. Further, attrition of teachers in the project schools was high; over 48% of teachers had left the schools at the end of the 4-year study. We examined the roles of the principal and IC Teams facilitator in program utilization. Descriptive data and case illustrations suggested that schools with high utilization among teachers had effective, stable facilitators who worked in collaboration with their principals. Implications for studying utilization of educational innovations by school staff are discussed.