This research synthesis from the National Comprehensive Center for Teacher Quality reviews the most recent research conducted on the impact of teacher characteristics on student achievement. The review aims to address the following questions: (1) What is teacher quality? (2) How can it be measured? (3) How important is it to student learning? (4) Do certain aspects of teacher quality have a stronger impact on student achievement for specific students, subjects, or grade levels? (5) How important is teacher experience? (6) How can teacher quality be better understood?