This is worrying but expected. Slightly surprised figures are not higher.
Schools have no or superficial use of PPE (especially primary schools) and essentially an ideal Covid incubator vector for asymptomatic super spreading.
There is also no systematic compulsory, accurate and frequent test, tack, trace and isolate. If testing was implemented at school more undetected positive cases would be recorded.
As expected at other similar settings schools are the ideal for Covid because:
daily
long duration
indoor
poorly ventilated (especially in winter)
overcrowded with unideal physical social distancing space
multi household mass gathering
younger children will be less compliant to social distancing, hand hygiene and self limitation of contact with touch points