This comparative study used the latest Trends in International Mathematics and Science Study (TIMSS) data sets and examined the relationship between professional development and student achievement. It found that although the national levels of access for students at the fourth and eighth grade levels to teachers who participated in professional learning in the United States were higher than the other countries, one third to one half of the fourth grades were taught by teachers who had no professional learning focusing on math instruction or curriculum. In addition, teachers’ participation in professional development was positively associated with higher student math achievement. This cross-national study provided empirical evidence highlighting the importance of investing in teacher learning for improving national educational quality.