This decision analytical model found that missed instruction during 2020 could be associated with an estimated 13.8 (95% CI 2.5-42.1) million years of life lost based on data from US studies and an estimated 0.8 (95% CI 0.1-2.4) million years of life lost based on data from European studies. This estimated loss in life expectancy was likely to be greater than would have been observed if leaving primary schools open had led to an expansion of the first wave of the pandemic.