These are two really good articles on re-opening schools. Very nuanced.
https://www.politico.com/news/magaz...pandemic-expert-analysis-politics-2020-355466
https://www.washingtonpost.com/worl...5fb3e6-c122-11ea-8908-68a2b9eae9e0_story.html
Both are pro-reopening (as am I, unlike my SWMBO), but both talk in nuanced terms about how you go about that and at different levels of schooling.
In general, unless there is a large outbreak in a community re-opening elementary schools shouldn't be a big problem. Now if a community has a large outbreak going on, then opening the elementary school makes less sense as it is simply one more interior building where people interact.
High schools are a more complicated matter as teenagers tend to be more contagious and there have been cases worldwide of outbreaks that involved HS level kids. This is a level where you may have to be more creative and in some places you may not be able to have them in person if outbreaks are bad enough.
It is also suggested that bubble routines may be one of the most effective mitigation measures for schools. Keeping kids in small pods or in some cases larger pods (they talk about as few as 6 in some cases, in the hundreds for others). This allows you to more effectively handle outbreaks without having to close the schools. You just end up quarantining bods with outbreaks if they occur.
The biggest issue facing the US right now as far as re-opening is we are simply at a much worse place than various European countries were when they started to re-open. Their cases per capita were a fraction of where the US is right now. They tended to open with various measures in place and then modified them as they figured out what was truly a potential issue and what isn't. That's the kind of thinking we need in the US right now so we can re-open our schools without increasing the risk of spread significantly.