This is basically a turn-based RPG, but to make each turn successful, you solve a math problem whose difficulty has been selected based on your past performance. They also play it at home, and I believe it has strengthened their math skills and given them a way to go at their own pace rather than that of the classroom. They earn levels, avatar mods, pets, and many other things to keep them coming back.
They also occasionally play chesskid.com at home as recommended by their chess teacher.
One thing I worry about is whether exposing them to such addictive games so early in their development will cause behavioral or even neurological side effects. I have heard about similar studies of teenagers revolving around drug use [1] but I don't know of any studies around video games (which also can cause addictive behaviors) and/or around children younger than teenagers. I would love to hear from others on HN about this.
