I too am having about 1/2 of my classes taking 1 to 4 weeks off at a time this summer. The one thing I have going in my favor is contracts and a billing service to help motivate them back into the DoJo when summer is over. We just have to hold on until the local school system starts back and then the DoJo will be full again. We are also doing 1 tournament a month to keep the ones in class motivated. It seems to give them another reason to train and makes them not want to go on vacation.