The Journal of American Medical Association prepared a statistical analysis and determined the following:
Years of life lost
“Missed instruction during 2020 could be associated with an estimated 13.8 (95% Confidence Interval 2.5-42.1) million years of life lost based on data from US studies and an estimated 0.8 (95% Confidence Interval 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.” (page 1).
Years of learning lost
“Missed instruction was associated with a mean loss of 0.15 (95% credible interval [Confidence Interval], 0.08-0.22) years of final educational attainment for boys and 0.12 (95% Confidence Interval, 0.06-0.19) years for girls.
You may read the entire report here.