The aim of the Central Michigan University Alpena-Montmorency-Alcona Teaching American History (TAH) Project has been to forge a model of professional development that would not merely improve teachers' knowledge of events, people, and dates, but to go beyond this to strengthen the understanding of the nature and practice of historical thinking, and to develop the ability to help students acquire this difficult set of skills. Through trial and error, it has been discovered that professional development is most meaningful and effective when the content of teacher leaming is strongly linked to the curriculum the students are learning. In primary source workshops, the project members have worked to combine sophisticated instruction in the history the participants will teach with practical strategies focused on developing effective, classroom-tested lessons and materials that reflect and teach both the content and structure of the discipline. This article describes the "uncoverage" approach that the authors have used as a model of professional development for history teachers. (Contains 8 notes.)