Warning message before navigating away from middle of lesson
When you're in the middle of a lesson and you accidentally click a link that will take you away from the page, close the window, or press back, it can be really annoying to have to start the lesson over. There is a very simple fix to this; Either: 1) Show a pop-up OK-Cancel warning 2) Save progress automatically
Note that if you almost fail a test, you can currently just close and restart it and you won't use up one of your tries.
@Kelvinsong - I disagree that this would be an 'annoying popup' because 1) you're rarely going to see it and 2) the majority of those who do see it probably have navigated away from the lesson by error and don't want to exit.