I always worry about whether my children will "forget" what they have learnt at school during the long summer break. I have read research that says studnets can lose up to 30 days of learning whilst they aren't in school.
If they get a summer cold when school starts again, they could be way behind every one else in their class.
My firend sent her children to a SCORE! Summer Program - Math Tutors last year and her kids have been near the top of their class all year.
You can be sure that I will be sending my two to the nearest SCORE! Summer Program... I won't tell them they are learning stuff and they won't care becuase they will be having too much fun.