The idea of reducing class sizes is very popular with the public, and there’s no organized interest group opposition to it. Consequently, one of the main things we’ve done in US education policy over the years is make class sizes smaller. But as Matthew Chingos writes for CAP, there’s precious little reason to believe this is a good use of money:
The evidence on class size indicates that smaller classes can, in some circumstances, improve student achievement if implemented in a focused way. But CSR policies generally take exactly the opposite approach by pursuing across-the-board reductions in class size at the state or federal level. These large-scale, untargeted policies are also extremely expensive and represent wasted opportunities to make smarter educational investments.
Large-scale CSR policies clearly fail any cost-benefit test because they entail steep costs and produce benefits that are modest at best. But what about reductions in class size at the district or school level? When school finances are limited (as they always are), the cost-benefit test any educational policy must pass is not “Does this policy have any positive effect?” but rather “Is this policy the most productive use of these educational dollars?” Assuming even the largest class-size effects in the research literature, such as the STAR results that indicate that a 32 percent reduction in class size increased achievement by about 15 percent of a year of learning after one year, CSR will still fail this test because it is so expensive. Reducing class size by one-third, from 24 to 16 students, requires hiring 50 percent more teachers. Depending on how much extra space schools have, new facilities may need to be built to accommodate the additional classes.
The better approach for any given lump of teacher compensation money is to plow it into ensuring that you’re recruiting and retaining the best possible teachers. In other words, just pay the teachers you have more money and hope that generates more and better applicants for positions in the future. It’s interesting to note, however, that the exact same trend exists in private and public schools. The public—whether as voters or as consumers—wants quantity over quality, probably because people like to pay for attention. But from a policy point of view, there are significant positive externalities associated with kids actually learning more while the customer satisfaction that comes from smaller class sizes doesn’t.