When do schools close for covid? The number of days a school should close is based on the size of the school and the number of cases. Despite those recommendations, if school officials can complete case investigations, contact tracing and cleaning in a shorter period of time, the length of closure may be shortened. Here's when schools are required to close based on size and the number of covid-19 cases: Low to moderate community spread Fewer than 500 students and staff: 2-4 cases, close for 1 or 2 days; 5 or more cases, close for 5 days 500 to 900 students and staff: 4-6 cases, close for 1 to 3 days; 7 or more cases, close for 5 days