I think the biggest problem both sides (although one side more than the other) have when talking about reopening schools is the tendency to lump in everyone under 20 into one category.
The timelines for reopening primary and secondary schools should look dramatically different, because Covid-19 acts differently between kids before puberty and adolescents.
https://www.statnews.com/2020/06/18/how-likely-are-kids-to-get-covid-19-scientists-see-a-huge-puzzle-without-easy-answers/We are finding that younger kids (5-12ish) tend to be spared from Covid-19 and also are just bad at spreading it.
However, teenagers seem to spread it at the similar levels as young adults, which honestly would make sense. Biologically, a 16 year old is closer to a 25 year old than a 6 year old.
The current outbreaks and anecdotal evidence from places such as Camp Kanakuk also support this idea.
Plus one of the biggest reasons to open schools is because parents have to work. This makes sense for elementary aged children, who probably shouldn’t be left alone for long periods of time, but teenagers are different (obviously) so the reasoning doesn’t apply to them as much.