The dramatic effects of kindergarten education: A controlled (!) experiment

The NY Times ("The Case for $320,000 Kindergarten Teachers", 27 July 2010) has just published an article about a very interesting controlled (!) experiment. The Harvard economists that conducted this unusual study (how many controlled experiments in education do you know about?) conclude that "a standout kindergarten teacher is worth about $320,000 a year. That’s the present value of the additional money that a full class of students can expect to earn over their careers. This estimate doesn’t take into account social gains, like better health and less crime."

If this is true, deciding on a kindergarten suddenly becomes a lot more significant that you may have imagined...

Some interesting excerpts:

How much do your kindergarten teacher and classmates affect the rest of your life?

Economists have generally thought that the answer was not much. Great teachers and early childhood programs can have a big short-term effect. But the impact tends to fade. By junior high and high school, children who had excellent early schooling do little better on tests than similar children who did not — which raises the demoralizing question of how much of a difference schools and teachers can make.
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Just as in other studies, the Tennessee experiment found that some teachers were able to help students learn vastly more than other teachers. ... Students who had learned much more in kindergarten were more likely to go to college than students with otherwise similar backgrounds. Students who learned more were also less likely to become single parents. As adults, they were more likely to be saving for retirement. Perhaps most striking, they were earning more.

All else equal, they were making about an extra $100 a year at age 27 for every percentile they had moved up the test-score distribution over the course of kindergarten. A student who went from average to the 60th percentile — a typical jump for a 5-year-old with a good teacher — could expect to make about $1,000 more a year at age 27 than a student who remained at the average. Over time, the effect seems to grow, too.
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The crucial problem the study had to solve was the old causation-correlation problem. Are children who do well on kindergarten tests destined to do better in life, based on who they are? Or are their teacher and classmates changing them?
The Tennessee experiment, known as Project Star, offered a chance to answer these questions because it randomly assigned students to a kindergarten class. As a result, the classes had fairly similar socioeconomic mixes of students and could be expected to perform similarly on the tests given at the end of kindergarten.

Yet they didn’t. Some classes did far better than others. The differences were too big to be explained by randomness. (Similarly, when the researchers looked at entering and exiting test scores in first, second and third grades, they found that some classes made much more progress than others.)

Class size — which was the impetus of Project Star — evidently played some role. Classes with 13 to 17 students did better than classes with 22 to 25. Peers also seem to matter. In classes with a somewhat higher average socioeconomic status, all the students tended to do a little better.

But neither of these factors came close to explaining the variation in class performance. So another cause seemed to be the explanation: teachers.

Some are highly effective. Some are not. And the differences can affect students for years to come.