In addition to Covid-19 transmission that takes place directly in schools, researchers also attributed the increase to “spillover” factors like parents being able to do more outside of the house if their kids are in school, and school reopenings sending an “incorrect signal” that “normal activities are safe again” to the broader community.
Seems obvious, but good to see a study that confirms this because there's so much denial about schools playing a role in spreading covid.
Forbes