Early September was always lovely. When I began working as a teacher in Halifax the Autumn term started mid-August - but there was a holiday mid-Sept. (for potato harvesting) and the weather was always great. It was a good idea - the kids settled in, knew their teachers and timetable and ploughed in to work on return. I experienced it, it worked well.
Bit depressed by current weather, but my birthday is 20/8 and I was born just before a major, major thunderstorm apparently - so it is normal. I think it will pick up. :)