Intel Teach to the Future was designed to provide a professional development experience that would prepare teachers to use technology with their students. The developers of the Intel Teach to the Future program began with two equally weighted goals, one related to the type of impact they wished to have and one related to the scale of impact. The first goal was to improve the integration of technology into K-12 classrooms. The second goal was to train 100,000 teachers in the United States in three years and to create "critical masses" of trained teachers within participating schools and districts. Intel anticipated that if a significant segment of a given teaching population was trained, this cohort of trained teachers would exert a strong influence on the overall school or district approach to technology. CCT's evaluation of the U.S. implementation of Intel Teach to the Future was conducted over three years and has drawn on a range of methods to investigate practitioners' response to the program, the local complexities of program implementation, and the program's impact in individual districts, schools and classrooms. The goal of the evaluation was to provide formative feedback to program staff in order to inform program improvement and to look longitudinally at questions of implementation quality and program impact. Findings from the three years of evaluation tell a multi-layered story about how Intel Teach to the Future has influenced teachers' knowledge and practices associated with the integration of educational technology into the classroom, and how the program has been leveraged within school districts to support teachers in their efforts. Intel Teach to the Future has been very successful in providing a positive, productive professional development experience to a very large population of teachers. (Contains 15 figures.)