This article documents evidence of nonrandom gender sorting across K-12 schools in the United States. The sorting exists among coed schools and at all grade levels, and it is highest in the secondary school grades. We observe some gender sorting across school sectors and types: for instance, males are slightly underrepresented in private schools and charter schools and are substantially overrepresented in irregular public schools, a large share of which educates students with special needs and juvenile justice involvement. Gender sorting within sectors and types is also quite prevalent and appears to be highest within the private schools (where single-sex schools are more common) and irregular public schools. We find that gender sorting is higher in counties that have higher shares of enrollment in private and nonregular public schools. This sorting occurs even though parents have similar stated preferences for school attributes for their sons and daughters.