The letter also requests school districts make accommodations for remote learning and cancel all extracurricular activities until in-person instruction resumes.
"Today, our community remains in the midst of a severe and uncontrolled spread of COVID-19. The fastest way to reopen our schools over the long haul is to flatten and -- just as importantly -- substantially bring down our hospitalization curve," said Hidalgo.
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"We must come to grips with the fact that in order to learn and grow, students must be healthy and safe. That means not setting arbitrary dates for reopening schools that provide false hope, dates this virus does not recognize or respect. Instead, our focus should be on thresholds and on developing measured reopening plans," said Hidalgo.