I made some changes to the interface for the kids based on this session, and I think the site is easier for them to use productively. When the games get tough or don't grab their imagination, though, motivation drops like a stone and can be hard to lift back up. This is partly dependent on age. I'm feeling that the classroom may be a better setting, therefore, than an after school club for best use, but both still have a role as not all teachers in a school would use it and those other kids should have a venue for it.
I'm running pilots in three schools this Fall, both as an after school club and in one case (at least) by a teacher using it in her third grade classroom. If any teachers out there read this and also want to participate, let me know.