What The Study Says Using 4th- and 8th-grade mathematics data from 2003, 2007, and 2011 Third International Mathematics and Science Study (TIMSS) assessments, researchers conducted a cross-national empirical study to examine teacher participation in professional development and its impact on student achievement. They conclude that, although 4th- and 8th-grade students in the United States had more access to teachers who participated in professional learning than similar students in other countries, one-third to one-half of 4th graders were taught by teachers who had no professional development in mathematics. They also conclude that teachers’ participation in professional development was positively associated with student achievement. Study description Despite an increased emphasis on the importance of professional learning and federal guidelines defining levels of investment in it for various