How do you know 4% isn't within the normal variability of the school age population? The authors implicitly conjecture a link to Covid related changes in educat

How do you know 4% isn't within the normal variability of the school age population? The authors implicitly conjecture a link to Covid related changes in education. They do not present any strong evidence. For example, between 2010 ad 2020, the population of 15 to 19 year olds increased 9% to 22m. The next cohort sizes drop down to 20m in 2010, so as the bumper crop of kids born between 2000 and 2005 age out of school, the overall population of school-age kids will shrink. Age 15 to 19 2010 20,219,890 2020 22,040,343 Diff +9% Age 10 to 14 2010 20,528,072 2020 20,677,194 Diff +.07% Age 5 to 9 2010 20,549,505 2020 20,348,657 Diff -1% Source: https://www.census.gov/prod/cen2010/briefs/c2010br-03.pdf https://www.census.gov/prod/cen2010/briefs/c2010br-03.pdf