Duolingo

Any level. Early level and the kids may not even know what questions to ask and they certainly can't fact check the AI. Late level and you need your own knowledge base to think critically and develop new things and use old things in new ways.

I second this question.

I mean hell, AI would just as soon mark a simple math solution wrong because it somehow thinks 1 + 3 and 3 + 1 aren't the same when obviously they are.