Well it's certainly only a single data point, but my mother has been teaching the exact same lesson plan for nearly 15 years now. Even if I were to be generous and say 50% of her summer break were devoted to preparing for the next school year, which is an absurd overestimation, that's still waaay more vacation time than just about anyone else in this country gets.
I certainly don't think there is anything at all wrong with teachers keeping more or less the same lesson plan year after year. From what I understand (and I have not personally studied this), the preferred teaching style in Japan and some other countries is to only make tiny incremental changes to lesson plans, year after year. Almost more of a scientific method or perhaps genetic approach to creating good lesson plans, as opposed to the more "artistic"(?) 'recreate it from scratch' method American teachers apparently use.
But really, my point is that "teachers don't really get breaks because they spend the summer revamping their lessons" thing is an old tired meme that really needs to be critically examined.
