Research increasingly demonstrates what common sense has long made apparent to educators and parents: Teacher quality matters--a lot. Teachers' knowledge and skills are the most vital in-school factors influencing children's learning. And, for children from disadvantaged backgrounds or troubled home environments, quality teaching is even more important. This paper analyzes promising new research about teacher quality and the incentives for teachers to do better. The authors assess current teacher quality approaches and offer recommendations to help policymakers modernize how teachers are prepared, hired, evaluated, and compensated. (Contains 3 endnotes.)