I am also a teacher and would say that three weeks would be a great amount of time to spend at WDW. But make sure that you do some of the "off the beaten path" stuff since 21 straight days in the parks might make you a little crazy. Good suggestions for WDW options- horseback rides at Ft. Wilderness, making smores and fishing at Port Orleans Riverside, tours in the parks (I'm slightly partial to Keys to the Kingdom since I used to give it) and anything else that interests your family under the recreation page. Also, some good non-WDW stuff would definitely be Kennedy Space Center (you may be able to catch a launch at that time of year) and Gator Land (somewhat corny but a truly "Florida" experience)! As for dining plan, I don't think I would do it for the whole time, but if you want to eat at several of the table service resturants you could figure out which ones you want to do and then schedule it for that number of days. I've eaten at them all (yes I know that sounds crazy but it was part of my job) and I think of 21 days of entree and desert at TS offerings would be a good way to make yourself sick. But maybe 10 restuarants might be good. The idea of getting a 1BR or 2BR in a DVC would be great not only for the kitchen but for the laundry as well. If you want two pretty "different" resort experiences (I'd hate to move more than once, even with Disney bell services help- they'll move your luggage for you) maybe AKL and SSR. Good luck and have a great time!