Analysis of the age profile of Covid infections, however, does not point to schools being especially important in the early-stage growth of the second wave. Although the report does also observe that ‘school closures can contribute to a reduction in SARS-CoV-2 transmission’.
But had schools played a big role you would expect to have seen a sharp increase in cases among children of school age a week or two following the return to the classroom. Instead, the ECDC noted that Europe’s second wave began with a sharp increase in cases among 19 to 39 year olds in mid August. Cases among 16 to 18 year olds also increased around this time, but the curve of infections among younger children rose much more gradually, in step with infection rates in the over-40s.
https://www.spectator.co.uk/article/what-role-do-schools-play-in-the-spread-of-covid-19-