Thanks! Yeah, I thought about adding hints but decided against it because I'm lazy. Yeah, the game was very fun to implement, as you can see in view source - it's my attempt to get UI architecture "right".
There's a back button, and lesson index is stored in a cookie so it should stick between reloads. I thought about adding jump labels, but the kids prefer going straight to "if" and "while" after finishing this thing. (Before it, they can't make sense of "while".)
I don't know whether it's better to give solutions right away, or if they should be revealed via a hint button.