It will spread through the schools and back to homes, infecting the parents/grandparents.
You need low active cases in the community before its safe to reopen schools, and even then you need to follow "common sense" rules to keep it from spreading.
Basically USA needs to get its new daily cases and active cases down to like ~2000 new daily cases accross the entire USA, and active cases down to like ~20,000-30,000.
The problem is the USA has:
2,100,000+ active (confirmed) cases
+70,000 new (confirmed) cases every day.
Thats like x100+ times more active cases than you want, and like x35 times more daily new cases as well (for safe school reopenings, equal to say in denmark).
Necro-bump this 2020: http://gamrconnect.vgchartz.com/thread.php?id=229249
Bumb in 2021: http://gamrconnect.vgchartz.com/post.php?id=9047071