A study of how middle and high school American history teachers adopted and maintained the use of research-based instructional practices is described as a model of professional development for social studies teachers. The teachers participated in a three-year project funded by the U.S. Department of Education's Teaching American History grant program. Teachers were observed, interviewed, and surveyed concerning their use of and feelings about twelve new strategies that were developed with a focus on pedagogical content knowledge. A variation on the Concerns-Based Adoption Model was used to measure the levels of use and stages of concern of the teachers over the three-year grant period and one year following the conclusion of the grant. Results indicate an increasingly high level of adoption and sustained use of the strategies, as well as the developmental nature of the process. Implications for professional development activities in history teacher education are presented. (Contains 9 tables.)