In this report we present findings from three years of evaluation research conducted by Research for Action staff that accompanied implementation of the Keystone Science Network (KSN). During that period, three cohorts totaling 185 teachers participated in KSN professional development activities and used the online resources developed by The Franklin Institute. The view of educational change as a learning process offered a conceptual framework for investigating how KSN assisted individual teachers to undertake new and challenging instructional practices and leadership roles in scaling up science education improvement in their schools and districts. Researchers conducted extensive field work and closely monitored KSN’s website and archived relevant data. In addition. teachers twice completed an extensive survey: (1) upon entering KSN and (2) near the end of the project’s third year, in April, 2002. This report finds that KSN’s web-based curriculum resources combined with the intensive professional development of the KSN summer institute and schoolyear colloquia were strong supports to teachers at all states of their learning about a standards-based approach to science instruction.