Hi,
Great question! There is not a way to do this at the moment, we will have to add functionality to log the user out. We'll get back to you with a solution.
In the meantime, the workarounds would be:
- Don't try to close the window. Tell the learner to log out instead (Settings > Log out).
- Tell your learners to launch the lesson in an incognito window. I don't know if I'd trust your learners to do this, though.