For schools to stay open and safe, President Biden said Thursday, they need to require vaccinations for teachers and staff, regularly test unvaccinated people and have universal masking. So far, the largest districts are succeeding at one — masking — but only a minority offer the others.

Out of 100 large districts, including the biggest urban districts in every state, nine in 10 are requiring students to wear masks, according to the Center on Reinventing Public Education at the University of Washington, which has been tracking districts’ responses to the pandemic since its start. Just one quarter are requiring teachers to be vaccinated. Fifteen are regularly testing students. And student quarantine policies are generally much less strict than they were last spring.

New York City public schools, which start Monday, are an anomaly on several measures, including the absence of a remote option and a more strict approach with quarantines.