Tween Proust loves to practice her Spanish with Duolingo. The app's gamification strategies work very well for her, getting her to play for 10-20 minutes per day. Is there a similar app she could use for expanding her English vocabulary?
I don't know the details of how Duolingo works. I know it keeps track of her daily streak (with generous amnesties for missing a day). It seems to rank her against other players in ways that she enjoys and aren't stressful. There appear to be other rewards. Importantly, the app gets satisfied after she plays for 10-15 minutes; it's not trying to keep her plugged in all day.
Is there something similar for intermediate / advanced English vocabulary? Doing it inside Duolingo would be ideal, but I don't think that's possible. We don't mind paying a modest monthly fee to get the right app. We're an Apple ecosystem family.