What do elementary teachers need to know and be able to do in order to successfully integrate the teaching and learning of data analysis and statistics as part of their instruction? This chapter discusses the design and implementation of a professional development program to help teachers integrate teaching about statistics in their instruction. This project included: the design of professional development curricula for use with teachers and with teacher leaders (statistics educators), a large-scale implementation program to provide professional development for both teachers and statistics educators using the professional development curricula, and a program of research and evaluation to assess the impact of the project and to surface research questions related to the agenda of the project. The focus of the program is the statistical investigation process: posing questions, collecting and analyzing the data, and interpreting the results. Evidence from participating teachers demonstrates the success of this program in supporting work with students and in promoting inquiry-based pedagogy.