Scholars from the American Institutes for Research analyzed findings from over 1,300 studies that potentially address the effect of professional development on student learning outcomes. The project was sponsored by the Regional Education Laboratory-Southwest (RELSW) and funded by the Institute of Education Sciences of the U.S. Department of Education. The findings from this comprehensive analysis, titled "Reviewing the Evidence on How Teacher Professional Development Affects Student Achievement" (Yoon et al. 2007), shed new light on the complex relationship between professional development and improvements in student learning. This research synthesis confirms the difficulty of translating professional development into student achievement gains despite the intuitive and logical connection. Those responsible for planning and implementing professional development must learn how to critically assess and evaluate the effectiveness of what they do.