After the study ended in 1989, researchers
conducted dozens of analyzes of the data. One
of the few points analysts agree on is that the
teacher’s assistants did not make any difference
to academic performance. Researchers
disagree about how long students have to be
in smaller classes to get a benefit, how big
that benefit is, when it becomes noticeable—
in other words, the collected findings have
yielded no consensus on the issues of real
interest to policymakers.
Jeremy Finn of the State University of
New York and Charles M. Achilles of Eastern
Michigan University found “an array of
benefits of small classes” in their review. Finn
calculated that students in the small classes
outperformed their counterparts in normalsized
classes by a fifth of a standard deviation,
and that this sizable jump in achievement
generally appeared by the first grade. Best of
all, this advantage seemed to persist into
upper elementary levels even after students
returned to larger classes. In order to appreciate
how big a difference there is in terms of a fifth
of a standard deviation, it is necessary to compare
two pupils first starting school who are as
average as it is possible to be statistically.
Both are in the 50th percentile, meaning that
half of the other pupils perform better than
those two and that half perform worse. One
student should be placed in a small class, and
the other in a normal-sized class. After a year,
the pupil in the small class will be in the 58th
percentile—in other words, the student will be
doing better than nearly 60% of his or her
peers—while the other student will still be
doing better than only 50%. Finn and Achilles
also found that the effect was stronger for
ethnic minority students, by a factor of two