Providing professional development for science teachers, Teachers in the Woods is a 6-week summer research experience in the national forests of the Pacific Northwest. Participants contributed to the scientific understanding of forest ecosystem functioning and later created local projects as forest ecology fieldwork for their students. Teachers were surveyed 3 times during the year and interviewed onsite. A standardized performance assessment measured student progress. The project changed teachers' approach to teaching and created greater motivation, confidence, knowledge, and skills in teaching biology and environmental science using field projects. Teachers attributed their success to enduring professional contacts with scientists and to their field experience. Evaluations also revealed major factors that affect the success of student field projects.