I don't think any of us are surprised to find out that teachers matter. That has always been obvious, but what I did find interesting--and even surprising--about the information coming from the study on a teacher's long-term impact on a student conducted by Raj Chetty and John Friedman of Harvard University and Jonah Rockoff of Columbia University is the degree to which teachers matter. (See the executive summary or full presentation video.) Their research shows that having a good teacher benefits a child long after that one school year and that measuring a teacher's "value-add" each year is one useful element in evaluating that teacher's performance.

According to Chetty, Friedman, and Rockoff, a teacher's "value-add" is defined as the average test-score gain for his or her students, adjusted for difference across classrooms in student characteristics (such as their previous scores).

These three professors conclude "that great teachers create great value, and that test-score based value-added measures are one useful input into identifying such teachers."

### What we'd like to hear from you

- What do you think about this research? (It is worthwhile

to watch the full presentation.) - What should be included in teacher evaluations?
- How long should a teacher have to improve an evaluation score?

*The graphics in this article were created by Caroline Madigan. *

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