Today's education policy places a high priority on improving teacher quality and teaching effectiveness in U.S. schools. Standards-based professional learning requires teachers to have deep subject knowledge and the most effective pedagogy for teaching the subject. States and school districts are charged with establishing teacher professional development programs, some with federal funding support, designed to address the significant needs for improved teacher preparation. The results of a national study of teacher professional development over a two-year period show that, while teachers are experiencing more professional learning than in the past, the country does not have strong data regarding its effectiveness to improve teaching and learning. What follows is a summary of recent research that measures effects of professional learning on student achievement and identifies characteristics of professional learning that produces positive results for teachers and students.