I started off using them for robotics - they make excellent WiFi-enabled controllers for the robots we use on our university undergrad first-year programming course.
Having gained experience with them in that context, I introduced them in my 12-year old son's school. The kids love them - they're small enough and cheap enough we can let the kids take them home (if a few don't come back it doesn't matter). That makes all the differnce - you can't learn programming in a couple of hours a week at school, but if you can start there and take the same computer home, you're far more likely to put in the hours to get good.
And, at least as good as the hardware, is the community that's grown up in the last year. Loads of excellent educational material is now freely available, and aimed at school kids. So much easier to get the teachers on-side when you can point them at all this material.