The U.S. Department of Education has issued updated guidance for schools and school personnel regarding the following issues that are impacted by COVID-19 related response measures including school closures. (Updated March 20, 2020).

Broad flexibilities provided to states to bypass ESSA mandated testing for the 2019-2020 school year due to COVID-19 national emergency. (March 20, 2020). Waiver application available here.
Fact Sheet: Addressing the Risk of COVID-19 in Schools While Protecting the Civil Rights of Students (March 16, 2020)
Protecting Student Privacy: FERPA and the Coronavirus (March 12, 2020)
Questions and Answers on Providing Services to Children with Disabilities During the COVID-19 Outbreak (March 12, 2020)
Fact Sheet: Impact of COVID-19 on Assessments and Accountability under the Elementary and Secondary Education Act (March 12, 2020)
CDC Interim Guidance for Administrators of US K-12 Schools and Childcare Programs: Plan, Prepare, and Respond to Coronavirus Disease 2019 (COVID-19)(updated March 12, 2020)

On March 13, 2020, the Department also issued updated guidance from the CDC on school closures.
CDC guidance on Considerations for School Closures (March 13, 2020)