  This paper empirically examines how the opening of K-12 schools and colleges
is associated with the spread of COVID-19 using county-level panel data in the
United States. Using data on foot traffic and K-12 school opening plans, we
analyze how an increase in visits to schools and opening schools with different
teaching methods (in-person, hybrid, and remote) is related to the 2-weeks
forward growth rate of confirmed COVID-19 cases. Our debiased panel data
regression analysis with a set of county dummies, interactions of state and
week dummies, and other controls shows that an increase in visits to both K-12
schools and colleges is associated with a subsequent increase in case growth
rates. The estimates indicate that fully opening K-12 schools with in-person
learning is associated with a 5 (SE = 2) percentage points increase in the
growth rate of cases. We also find that the positive association of K-12 school
visits or in-person school openings with case growth is stronger for counties
that do not require staff to wear masks at schools. These results have a causal
interpretation in a structural model with unobserved county and time
confounders. Sensitivity analysis shows that the baseline results are robust to
timing assumptions and alternative specifications.
