You used to be able to skip around lessons on Duolingo, but then they changed it. That's when I quit using them. I know how I learn and I like to go through a lesson and If I don't do well, I'll go to the next lesson and go back and redo the one I failed later.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store