Few education reforms receive as much public approval as reducing class size. At least 21 states have adopted class-size-reduction programs since 1984.[12] Washington state voters passed a ballot initiative to further the cause in 2000. And Congress voted in 1999 to set aside $1.2 billion dollars to subsidize such programs. California alone dedicated an additional $1.5 billion to shrink classes from just under 30 to 20 students.[13] Teachers, too, are solidly behind class-size reduction. The American Federation of Teachers supports significant class-size reduction,[14] and the National Education Association (NEA) has a goal of reducing all classes to 15 or fewer students.[15]

Does reducing class size produce the kind of improvement we seem to expect? It certainly seems reasonable to assume that the more attention teachers can focus on each student, the better students will do.

Unfortunately, what seems reasonable in theory doesn't always hold true in practice – that's why we do studies. Recently, the journal Psychological Science in the Public Interest published a very thorough investigation that sifted through the reams of available literature on the subject.[16] After poring over decades-worth of research, the authors concluded that very little can be said with regard to higher achievement as a result of smaller classes. Very tentatively, they suggest that reducing class size to 15 students may improve test scores in kindergarten and possibly the first grade. Though that gain persists in later years, no added benefit seems to be achieved from reducing class size beyond this point.

In other words, there is reason to believe that reducing class size in kindergarten and perhaps the first grade may do some good, but in older grades there is no evidence this will improve achievement. And even such a weak endorsement is qualified by the study's authors, who warn that class-size achievement effects may not be generalizable to other schools and students.

It seems that we have thrown our support behind smaller classes not because of the evidence, but because they seem like a good idea, and because they are less controversial and easier to implement than alternative reforms (if sometimes more expensive). Shrinking class sizes across the board allows us to feel like we're doing something to help our kids. But if we really care about solving the serious educational problems affecting all our children, we will have to look beyond our feelings and ask what truly works.