The middle of August.
The day after Labor Day in Sept
When I was in elementary school it was in September. By the time I was in high school it was late August.
My niece's son started 2 weeks ago. They are doing year round school.
In September. The Tuesday after Labor Day Monday.
Always the first week of September, following Labor Day.
Late August for grade school. College always started in September.
September here in the UK.