Post below this one, so scroll down!
I have loved summer reading clubs since I was 6 years old. I taught myself to read (w00t w00t Electric Company!) and did my first library reading club the summer after Kindergarten. I still remember the theme--a race, with a paper horse with my name on it that advanced around a track. We could write out our book reports, or sit down with a librarian and tell her our reports orally--I always chose oral reports because they were faster. I read 60 books that summer.
It thrills me that my own kids love the reading club at our library, and have taken to it like ducks to water. My older son lost no school reading levels over the summer last year (I think he actually gained one) because of reading club.
As I was playing with DreamBox with my younger son, it occurred to me that math video games are the math counterpart to reading clubs. They maintain the competition-with-yourself aspects of the reading clubs, and give kids the joy of using their brains in a non-pressured situation. Since video games are fun, it's not "homework," and the kids feel like it's a treat instead of an assignment. I'm betting my older son won't lose any school math levels this summer from playing DreamBox. I'll let you know in the fall.