I think this application is great! 30 years ago, I emigrated to US when I was 13 years old. I knew only 26 letters and maybe one hundred words. I had to bring up my language skill up to high school level within few years so I can graduate high school and kept my grade good enough in order to enter college. Retain vocabulary through reading is what works for me. It is difficult to remember words without context. Back then, I started with toddler's book then progressed to young adult science fictions. I enjoyed the fastest progress with young adult fictions. I think what you created is very helpful for kid. I will try it out with my son. I am back to Asia now and try to teach my son English.

Nifty! Has it been working out for users?

Any thoughts on whether extending it to animated images might not/work? Might help with verbs?

Bigger picture, perhaps imagine a UI with two panes. One the regular app. And the other, a... bantering play space, where the app can do sciencey interactive jazz improv on what's been said in the regular app. Any feel for whether this would work, or be too distracting? Has anyone seen something like this?