This study sought to examine the impact of teachers' participation in an extended period of embedded professional development (PD) emphasizing teachers' use of assessment for learning practices (AFL) in extended problem based units of instruction within a comprehensive AFL framework. The extended and comprehensive approach of using both course work and learning teams provided them with an in-depth understanding of these practices and the opportunity to apply that understanding in their daily work with their students. The eight elementary grade teachers' assessment practices changed dramatically as a result of the PD provided. Those changes were maintained even after external support was withdrawn, and teachers intended to continue the use of AFL strategies in the future. "Survey: Knowledge and Use of Assessment and Assessment for Learning Strategies" (Appendix A) is appended. (Contains 4 tables.)