There are plenty of studies on this subject from across the world now.
Here is one from the CDC for a study period ending on September 19th.
https://www.cdc.gov/mmwr/volumes/69/wr/mm6939e2.htm#T1_down
Of course, your interpretation of the data is that the risk is acceptable. The interpretation of the majority of disease experts and medical experts is that the risk is not acceptable, I'll go with the mainstream medical experts. Especially when the medical experts point out that most school systems are not even following basic COVID safety standards.
Of course there are ways of re-opening schools with reduced student populations (only 1/2 or 1/3 students as a time) and proper precautions (masks, reduced contact, etc.) that greatly reduce the risk and make attending schools safer. But many school systems are not following these recommendations -- and many times they are hard to enforce with the students.
There needs to be national standards how schools must operate on-campus for COVID that every school system in the country must follow. Of course, Trump nixed the CDC providing national standards to be followed for safety in schools. The standards must include the criteria for when schools must close again -- including when the positivity rate in their local community goes above a set threshold