We are going all year. We go 5 days a week in September (with two weeks off in the middle for the fair), 4 days a week October-November when our co-op meets with a 4 day weekend for Thanksgiving, then back to 5 days a week until the middle of December (two weeks off for Christmas and New Years), January-February we do 4-5 days a week, co-op starts again in March so back to 4 days a week, May is back to 5 days a week, and June-August we go 3 days a week with a week off thrown in there somewhere depending on what is going on. Whew!
We used to school all year round and then we quit the past couple of years. I made the decision to at least do 3 days a week in the summer because by the middle of June my boys have played every video game, seen every allowed movie, built every known (and unknown) Lego creation, and have resorted to entertaining themselves by annoying each other. That and it's too hot to do much outside until later in the evening, so we will sit inside, in front of the AC and get some work done. They have other summer activities as well, and the 3 day a week schedule works with those activities too.
I also sell candles at local shows so I need to be really flexible as far as that goes summer through the Christmas season.