With an initial 10-year commitment from Merck & Co., Inc. the Merck Institute for Science Education (MISE) was founded in 1993 to demonstrate that virtually all students could reach high levels of scientific literacy. Shortly thereafter, MISE formed partnerships with four public school districts -- Linden, Rahway, and Readington Township in New Jersey, and North Penn in Pennsylvania -- where Merck has major facilities and a history of providing employee volunteers and supporting local science education initiatives. These district partnerships quickly merged into one multi-district Partnership. MISE's approach to improving science teaching has been systemic, addressing both policy and practice in the partner districts. MISE has helped its partners plan strategically, select highquality instructional resources, support teacher learning, and carry out instructional and curricular reforms. Working together, MISE and its partner districts have developed and implemented a shared vision of good science instruction based on national and state standards. This vision has been the basis for the design and delivery of professional development for teachers and administrators. Sustained by the Partnership since 1994, this professional development program has helped the partner districts make significant reforms in the teaching of science and mathematics. In 1993, MISE contracted with the Consortium for Policy Research in Education (CPRE) at the University of Pennsylvania to evaluate the effectiveness of its work with the four districts. CPRE has documented the activity and progress of the Partnership for a decade and has issued a series of reports on its impact. In this report, we assess the Partnership’s approach to professional development. Specifically, we address the following questions: 1. How has the Partnership’s professional development measured up against the emerging standards for professional development? 2. Has participation in Partnership professional development resulted in increased teacher content knowledge? 3. Has participation in Partnership professional development led to changes in instructional practice? 4. Has participation in Partnership professional development resulted in improved student achievement? 5. Has MISE’s strategy strengthened district capacity to support the improvement of teaching? 6. What lessons can be learned from the experience of MISE and the Partnership with professional development?