What does the data say about the importance of teacher quality?

1. Project STAR was an experiment designed to test the effect of class size. The experiment found that students assigned to small classes earned $4 more per year. If you add demographic controls, students assigned to small classes earned $124 less per year. (more)

2. You can use Project STAR's data to (non-experimentally) test for other effects. When you do, almost all measures of teacher quality fail to increase adult earnings:

The few other observable teacher characteristics in the STAR data (degrees, race, and progress on a career ladder) have no significant impact on scores or earnings.

3. There is one measure of teacher quality that does matter: Whether the teacher has more than 10 years of experience. Chetty et al. find that students assigned to a kindergarten teacher over this experience cut-off eventually earn $1093 extra dollars per year. But bear two reservations in mind. (a) The t-stat is only 2.4 - extremely low for a non-experimental test with 6005 observations. (b) If you measure experience in years, rather than using their binary "more than 10 years of experience" variable, the point estimate is a statistically insignificant $57 per year.

4. Teacher experience only matters in kindergarten:

The effect of teacher experience on test scores is no longer statistically significant in grades 1-3. Consistent with this result, teacher experience in grades 1-3 also does not have a statistically significant effect on wage earnings.