kitchen table math, the sequel: Class-size Reduction and America's Misplaced Priorities

Tuesday, March 27, 2007

Class-size Reduction and America's Misplaced Priorities

The Common School: A Question of Scale: Class-size Reduction and America's Misplaced Priorities

Via Eduwonk... new blogger "Dewey", who is reputed to be a minor education wonk, makes the case that class size reduction would have a tiny effect on educational outcomes.
But the really mind-blowing results come when you start comparing a class-size reduction to giving students a teacher with a reasonably good (though not unlikely) combination of teacher credentials (estimated by adding the relevant values in the table above). Clotfelter and Ladd do their own estimates of this sort and come up with a combined effect size of 15% - 20% SD for math (and 8%-12% for reading) of a well- credentialed teacher.

The first time I read this portion of the study I said to myself, "Yeah class size is less important,” but that finding is not particularly novel to anyone who follows this sort of research. But when I decided to actually compare how much less important class size is my jaw dropped. The effect size of teacher credentials is 8 to 10 times that of a major class size reduction in math and 6 to 8 times as big in reading!!!
He figures it would take approximately 150% billion dollars in increased salary costs (if the improvement for reducing students is linear that is), for a net benefit of 1.6% to 4% SD in math instruction. He then goes on to propose several novel ideas about how that money could be better spent for a much more significant educational outcome.

My only observation:

Isn't it possible that reducing class size would actually have a negative effect, instead of a small positive one?

We already have difficulty attracting teachers into teaching, especially in math and science. Doubling the number of teachers would have to entail reducing standards and quality.

Wouldn't the net effect of the lower average teacher quality more than cancel out the small benefits of reduced class size?

Go read the full post and if your statistically savvy, analyze his data and conclusions.

Pretty damn good for his 2nd post though.

(Cross posted at Parentalcation)


Instructivist said...

The merits of class size reduction cannot be discussed without taking into account the quality of the student body. With well-behaved and motivated kids, it's less of an issue. With a room full of the behavior disordered -- a common occurrence in big city schools -- it's a huge issue.

A cheaper alternative to class size reduction would be to segregate the dysfunctional. It's unconscionable to allow a handful of miscreants to prevent those who want to learn from learning. But entrenched egalitarian ideology throws roadblocks in the way of this sensible solution.


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Tracy W said...

I understand that the problem of finding enough good teachers if you reduce class-sizes is pretty significant. I remember discussions of the California experience that blamed the lack of an improvement in schools when class-sizes were reduced to that problem.

Dewey's own figures show that an experienced teacher (3-5 years of teacher experience) is worth about a 7.2% - 9.1% of a standard deviation impact on math achievement (though there may be an endogeneity problem - teachers may be more likely to stick around for at least 3-5 years if they're naturally good at the job anyway).

Engelmann's results from DI experience implies that to some extent Dewey's suggestions are a side-show, you can get great improvements by teaching average teachers the tools to do their job well.

Unknown said...

Yow! A black background! My eyes! My eyes!

Instructivist said...

See what I mean about segregating the dysfunctional: