Thousands of American teachers and students have already gone back to school, prompting a backlash from parents campaigning to "reclaim" summer.
Driven by pressure to get an early start on grooming pupils for high-stakes tests, schools in Miami reconvened last week - their earliest return date yet - along with most other Florida schools. In parts of Georgia and Arizona, term started three weeks ago.
Last year, 71 per cent of US schools went back before September, versus 58 per cent in 1992-3, according to Market Data Retrieval.
But parent groups angry that the trend is eating into family holidays and business groups protesting at lost tourist revenue, have successfully lobbied to push back start dates in multiple states.
Wisconsin recently laid down a mandatory post-September 1 back-to-school date, while Minnesota ruled last month that its schools cannot restart before the first Monday of September. A vote on similar measures is pending in Michigan and battles loom in Texas, Florida and Georgia.
"Our summers are being stolen," said Jeanette Henderson of Save Our Summers, a pressure group in South Carolina.
But the controversy over start dates may be obscuring a larger issue. To start back sooner so that they can fit in more study time before winter and springtime testing, many US schools are simply breaking up earlier, often in May. This leaves untouched the traditional three-month duration of US school holidays, frequently cited as a factor in "summer learning loss", in which pupils regress for lack of educational stimulation.
The problem is particularly acute among poor students with limited educational resources at home, and is a primary cause of the achievement gap between minority students and their peers.
To counter this, growing numbers of schools are adopting year-round schooling, cutting summer holidays and spreading breaks more evenly throughout the year.