The Peabody Fellows in Earth Science program was a professional development opportunity for middle and high school teachers to enhance their knowledge of, and teaching skills in, the Earth sciences. It combined a summer institute and academic year workshops with the production of new curricular resources on the interpretation of landforms in Connecticut. Teachers implemented these materials with the aid of an accompanying classroom kit. The program included in-depth evaluation of the project outcomes for teachers and students; focused on tectonic processes; and on erosion, weathering, and glaciers. Forty-seven teachers participated in the institute, 30 taught the full curriculum, and 21 completed all the evaluation activities. Teachers reported that they had significantly increased their geoscience content knowledge as well as their ability to teach geoscience-related skills, particularly in guiding students to make observations and inferences about the local landscape. In the majority of cases for teachers that completed all evaluation activities, there was a significant increase in student performance in at least one learning goal as a result of the teachers' participation in the program. These data show this type of informal-formal educational initiative can be highly successful in improving teacher competence and student learning in the geosciences. They also provide evidence that positive proximal outcomes for the teachers are reflected in the ultimate outcomes for students.