There are no absolutes at this point, we need to think how to improve things incrementally:
ujm: children are *NOT* a major spreader
indeed, probability of passing the virus is lower with age. Teenagers are same as adults. Having more close contacts increases that. So, if you are in a community where nobody is careful, then (elementary/middle) school are not a priority. But, where there are some adults who are more careful, children in schools are a relative high risk.
Ari256: probably need to focus more on providing families tools to teach their children at home, whether it is one day a week or anything else. The less children are at school at the same time, the better.