Federal law emphasizes the need for states and districts to ensure that "all" students--particularly at-risk students, minority students, and students in high-poverty areas--have access to highly qualified, experienced teachers. But is it sufficient for a teacher to have "paper" qualifications and teaching experience? After all, appropriate degrees, certification, and experience may be important at a minimum, but do they guarantee quality teaching? This synthesis of the research on teachers and their contribution to student achievement found that a number of studies cite a few areas of teacher quality in which research shows convincingly what matters, whereas the inconsistency of other findings indicates that much is still to be learned. Organized using a framework of inputs, processes, and outcomes, this synthesis is a "one-stop shop" for researchers and policymakers interested in the science behind claims about the link between teacher quality and student academic achievement. Appended are: (1) Teacher Quality Variables Utilized; (2) Data Sources Used to Define Teacher Quality; (3) Summary Table of Studies Examined; and (4) Further Discussion of Effect Sizes. (Contains 1 figure and 18 footnotes.)