by William J. Bennett, CNN Contributor
Editor's note: William J. Bennett, a CNN contributor, is the author of the newly published "The Book of Man: Readings on the Path to Manhood." Bennett, the Washington fellow of the Claremont Institute, was U.S. secretary of education from 1985 to 1988 and was director of the Office of National Drug Control Policy under President George H.W. Bush.
(CNN) - A good teacher not only improves a child's test scores in the classroom, but also enhances his or her chances to attend college, earn more money and avoid teen pregnancy, according to a new seminal study.
The study, conducted by economists Raj Chetty and John N. Friedman of Harvard and Jonah E. Rockoff of Columbia, tracked 2.5 million students over 20 years from a large urban school district from fouth grade to adulthood, making it one of the largest and most consequential educational studies in recent years.
Their findings focus on the long-term impact of teachers based on their "value-added" ratings. This refers to the average test-score improvement for a teacher's students, adjusted for differences across schools and classrooms such as prior test scores. Evaluating teachers based on student performance has been the subject of much debate among teachers, unions and policymakers.