"It may be schools"
I'd be surprised if schools are driving or accelerating infections to a major extent, compared to say reopening some sectors of the economy
School cases seem to be a reflection of community level infections and any effect on R is more the sheer number of children and adults together
e.g. The small German state of Mecklenburg-Western Pomerania started ft schools on 3 August, so has had 4 weeks.
Their 7-day incidence then was 2.1 / 100,000 and rose briefly to 2.9, but has been falling since to now only 0.8 / 100,000
They have had the least precautions of any German state and seen only a few cases in schools - although they closed schools for only 1 case (!)
The initial rise seemed to be caused mostly by returning holidaymakers and parties, both of which have tailed off since school restarted - firms have their annual summer holidays during school hols.
However, states with much higher starting levels in the community saw far more cases in schools and far more school closures, e.g. Berlin, although again closing schools for only 1 or 2 cases.