Do school uniforms make students behave better or get better grades? Researchers in the United States followed about 6,300 children from kindergarten to the upper grades of elementary school. Children at schools with uniforms did not behave clearly better.

Their attendance was not clearly better, either. Other studies found almost no effect on grades. So wearing a uniform does not change students much. People can still discuss uniforms for other reasons, like cost.

Supporters of school uniforms say they make schools calmer and help students focus. Researchers at Ohio State University tested this idea using data on about 6,300 American children, who were followed from kindergarten through the upper grades of elementary school. Compared with children at schools without uniforms, those at uniform schools did not show clearly better social skills, fewer behavior problems, or better attendance. This was true for both public and private schools.

However, children from low-income families had slightly better attendance at schools with uniforms. An older study of high school students even found a negative link between uniforms and grades. So there is little evidence that uniforms improve students' behavior or learning.

School uniforms are often defended on the grounds that they promote discipline and academic focus, yet the empirical support for these claims is surprisingly thin. Using a nationally representative sample of about 6,300 American children followed from kindergarten into the upper elementary grades, Ansari and colleagues found that students at schools with uniforms did not differ meaningfully from their peers in social skills, behavior problems, anxiety, or attendance, in either public or private schools.

The one exception was slightly better attendance among children from low-income families. Earlier research on tenth graders detected no direct effects of uniforms on attendance, behavior or substance use, and even a negative association with achievement. A before-and-after study of schools that introduced uniforms reported modest gains in secondary school attendance but no major effects on grades. Analyses of international PISA data, meanwhile, linked uniforms to better listening.

However, schools that adopt uniforms may already emphasize discipline, so it is unclear which causes which. Almost no studies have randomly assigned uniforms, and evidence from Japan, where most secondary schools require them, is scarce. Debates about uniforms might therefore be more productive if they focused on cost, convenience and belonging rather than grades.