Also a teacher so I have to go in the summers too. My preference is to push it as late as possible, because July is the big travel month for the tour groups and they tend to make things more crowded (in surges) and fast pass to not always work as planned. However, once it gets to be late June, it's just hot no matter what. If you are back to school later in August, you will find most of the southern schools go back early August, so it will slow down towards the end of the month.
I was there mid-July this summer, and we had hot hot weather with daily rain, but manageable crowds if you plan. (Go early, get out mid-day, swim, etc. and go back in evening).