Evelyn Davies, headteacher at Coldfall Primary School in North London, told the Mirror why she is concerned about the plans.
Ms Davies- whose school is rated Outstanding - says she may not be able to expand pupil numbers in the way the government has outlined from 1 June if a risk assessment suggests that pupils and staff could not be kept safe.
She has expressed concerns about how she can run her school, which normally has 680 pupils and 90 members of staff, safely within the new guidelines.
Ms Davies told the Mirror: "We should not open schools until we have the science to show that it's ok to do so. "I think there's very confusing mixed messaging about what's safe.