How many is too many?

Cases are continuing to spike in Duval schools. However not many classes are closing. We went into the school year thinking that the right precautions were being taken to keep cases low. The total opposite has happened. There are 466 COVID cases in Duval county: 322 students and 144 staff. So the question remains how many cases are too many cases? How many cases do there have to be to close down schools?