Actually, teachers don't get the whole summer off.  (I used to date one.)

The principal is going to want them all back in the school a week to ten days before the kids come back.  They have a lot of staff meetings during that time.  And teachers (the good ones anyway) are going to use some of that summer time to do prep work for the coming year--getting the classrooms ready, doing some advance lesson planning, going over the children's files, and so on.

During the school year, the children may only be in school from nine to three, but the teachers are there before and after.  And they take work home or come into the school to work on weekends.

So please don't judge the teachers' workload by the amount of time your kids spend in school.