This longitudinal study examined the extent to which teachers' participation in a 3-year professional development program enhanced their self-efficacy and prompted changes in science instruction in the early elementary grades. The study used a mixed-methods design, and included 39 teachers who taught in kindergarten, first grade, or second grade classrooms in rural school districts. Data sources, administered pre-program and at the end of each year, included a self-efficacy assessment and teacher survey. Interviews and classroom observations provided corroborating data about teachers' beliefs and science instruction. Results showed significant increases in teachers' overall self-efficacy in teaching science, personal efficacy, and outcome expectancy efficacy during the 3 years. Gains in self-efficacy were correlated with changes in reported instructional practices, particularly student participation activities. However, changes in self-efficacy tended not to be correlated with changes in instructional time. Contextual factors beyond teachers' direct control, such as curricular and testing requirements in mathematics and language arts influenced time allotted to science instruction.