David and Goliath: Underdogs, Misfits, and the Art of Battling Giants

the data. In this study, I found estimates
that are very precisely estimated around
the point zero. I got a precise zero. In
other words, there is no effect.”
This is just one study, of course. But
the picture doesn’t get any clearer if you
look at all the studies of class size—and
there have been hundreds done over the
years. Fifteen percent find statistically
significant evidence that students do
better in smaller classes. Roughly the
same number find that students do worse
in smaller classes. Twenty percent are
like Hoxby’s and find no effect at all—
and the balance find a little bit of
evidence in either direction that isn’t
strong enough to draw any real
conclusions. The typical class-size study