Watch your actual position on the leaderboard every time you end a lesson
Every time you end up a lesson, see how you are rising on the leaderboard with the new points you just earned, like "You are now at 9th position on your country leaderboard!" or "You are just 20 points down the 28th position globally!".
I think that will motivate users to keep learning more lessons so they can reach higher positions without needing to leave lessons to check their new position.