by Raj Chetty - Harvard University, John N. Friedman - Harvard University, Jonah E. Rockoff - Columbia University | http://bit.ly/zV4vEr
A teacher's "value-added" is defined as the average test-score gain for his or her students, adjusted for differences across classrooms in student characteristics (such as their previous scores). Is teacher value-added a good measure of teacher quality?
When a high value-added (top 5%) teacher enters a school, end-of-school-year test scores in the grade he or she teaches rise immediately...
... and students assigned to such high value-added teachers are more likely to go to college, earn higher incomes, and less likely to be teenage mothers. On average, having such a teacher for one year raises a child's cumulative lifetime income by $50,000 (equivalent to $9,000 in present value at age 12 with a 5% interest rate).
The gains from replacing a low value-added (bottom 5%) teacher with one of average quality grow as more data are used to estimate value-added. The gains are $190,000 with 3 years of data and eventually surpass $250,000 in present value at age 12. If future earnings are not discounted, cumulative earnings gains surpass $1.4 million per class.
We conclude that great teachers create great value, and that test-score based value-added measures are one useful input into identifying such teachers.
●● smf's 2¢: This study is a real study, not a ginned-up press release from ®eform, Inc. Please read the executive summary – and if you have the stamina, patience and educational background have a go at the full report.
The primary conclusions are inarguable:
- Great teachers create great value
- Test-score based value-added measures are one useful input into identifying such teachers.
That said, it creates Lake Wobegonian expectations: 100% of students, be they White, Asian, Black, Hispanic, Native American or other; wealthy, middle class or mired in socio-economic chaos - cannot and will not get the 5% of the best teachers all the time. What this report confirms is that the rare great teacher that a student gets makes a great difference …and it points out that the grades between 4-8 (ie: middle school) are probably most critical.
Those of us who were so lucky knew that.
- What is unclear is whether this study and the previous study – which cite similar numbers - were based on the same data in the same school district