On February 12, 2021, the CDC released school reopening guidelines titled CDC’s Operational Strategy for K-12 Schools through Phased Mitigation. Here is the link to them: https://www.cdc.gov/coronavirus/2019-ncov/downloads/community/schools-childcare/K-12-Operational-Strategy-2021-2-12.pdf

In addition, here is an overview sheet that CDC put out as well: https://www.cdc.gov/coronavirus/2019-ncov/downloads/community/schools-childcare/Operational-Strategy-for-K-12-Schools-through-Phased-Mitigation.pdf