In this article, we describe a conceptual framework for in-service professional development--the Whole Teacher approach. A significant departure from the traditional approach to professional development that speaks primarily to teachers' acquisition of knowledge and skills, the Whole Teacher framework emphasizes promoting all aspects of a teacher's development, including attitudes, knowledge, and practice. Putting the framework in operation, we describe a project proven to be effective in helping to develop teachers' competence and increase children's performance in early mathematics. We focus on how the Whole Teacher framework guided the project's design, implementation, and program evaluation. The article concludes with a discussion regarding the significance of the Whole Teacher approach to teacher professional development. (Contains 2 figures and 2 tables.)