Great teachers make a profound difference in the lives of children. Each of us can remember the personal qualities of a great teacher whose influence stretches into our adulthood--or who gave our own children a solid start in life. But these elusive qualities are hard to measure. It's even harder to use them to predict who will become a great…

For all the conflict generated by various K-12 education reform efforts, there is one principle everyone agrees on: teachers need to know the subject matter they teach. This principle makes sense to parents, educators, and policy makers alike. On the importance of a teacher's knowledge the views range from those who believe subject knowledge to be…