embodies the most stunning finding to come out of education research in the past decade: more than any other variable in education—more than schools or curriculum—teachers matter.

Parents have always worried about where to send their children to school; but the school, statistically speaking, does not matter as much as which adult stands in front of their children. Teacher quality tends to vary more within schools—even supposedly good schools—than among schools

The results are specific and surprising. Things that you might think would help a new teacher achieve success in a poor school—like prior experience working in a low-income neighborhood—don’t seem to matter. Other things that may sound trifling—like a teacher’s extracurricular accomplishments in college—tend to predict greatness.