An Earth science professional-development program for in-service middle- and high-school teachers increased participants’ content knowledge about weather, climate, and climate change in addition to increasing their confidence in their assessment and teaching skills. The curriculum and funding gave them time, funding, and the help of content and pedagogic experts to build and test new lesson plans on these topics. During the summer workshop, the teachers participated in field trips, hands-on laboratory experiences, and cooperative inquiry projects. They studied weather and mechanisms that determine climate during the first week. The second week focused on geologic time and changes in the Earth system that drive climate changes on long timescales. The major topic for the third week was anthropogenic climate change. During the workshop, the teachers designed lesson plans for multi-day units on workshop topics. The teachers took a content pretest at the start of the summer workshop and a post-test at the end. Their average score increased from 38.1% to 75.6%. The follow-up program included three meetings and two classroom visits by a veteran teacher during the subsequent school year. The participants taught their lesson plans and administered pre- and post-tests that they had designed to their own students. Their class scores showed normalized gains ranging from 16% to 88%. Surveys taken at the beginning of the summer workshop and the end of the follow-up program indicated an average increase in their confidence of their ability to teach science and in their willingness to employ hands-on, cooperative, and inquiry learning techniques in their classrooms.