Uniform use in public schools is rising, but we know little about how they affect students. Using a
unique dataset from a large urban school district in the southwest United States, we assess how uniforms
affect behavior, achievement and other outcomes. Each school in the district determines adoption independently,
providing variation over schools and time. By including student and school fixed-effects we find evidence
that uniform adoption improves attendance in secondary grades, while in elementary schools they
generate large increases in teacher retention.