Will be possibility of choosing lesson length here? For someone 20 can be too long for another one it can be too short.
I think it will be nice to have possibilites of something like: lesson with length 5 will give you 1 point, 10 -> 3, 20 -> 10 (current only option), 40 -> 40, etc or something like that.
I must tell that 20 is too long for me and if I fail third time to complete lesson it makes me stop for days. So I would be really glad if there will be shorter lessons like length 5 with one heart (even if it will be for 1 point) so I can see any improvement.
It can also be a real pain when you just need a couple of points to master and close off a leg on the Skill tree. I've noticed that even if you only need 3-4 points, you still have to work through all the questions (that should be worth 10 points). At the end of the lesson, you are only awarded those 3-4 points you needed to master it. Cheat! The lesson should end as soon as you have accumulated the necessary points.
You should also really be able to save progress in a lesson. If you close the window (even accidentally, which is really annoying) before you finish, you lose all your progress. Plus if you're testing out a skill but have run out of hearts, and you don't want to use up your try, you can just close the window and it doesn't count and you can start over.