I'm not sure when school began to start before the first Wed after Labor Day, but it's bullshit. Adding a few days to the school year does nothing to improve a child's education.
Summer activities with friends is far more valuable than moving the rituals of the first few days of school up even just a few days.
"When does school start" should never be a valid question. The Wed after Labor Day should be the only answer.
Oh ... and the change in the starting date for school is what killed the Jerry Lewis Telethon.
</rant>
I'm not old enough to provide feedback to your last point, but I agree with everything else you said.
About a decade ago, a previous head of school incrementally added time to our school year to the tune of once his seven year tenure was over,
poof we added three extra weeks. Famously, he once told me in private
if it weren't for the board, I would probably put in place a year-round calendar as he justified his reasons for families and teachers. The idiot spent two whole years in the classroom.
What's weirder is that our highest-esteemed competitors follow a Labor Day to Memorial Day schedule, so it's not uncommon to have partially filled classrooms prior to Labor Day and post Memorial Day.
At least, on the summer end its mostly remedied: our last day w/ kids is June 6th and teachers stick around for three days after that. However, I do not know a single private school teacher in the area who had to return to work as early as us, this Tuesday w/ kids coming the following Tuesday.