I like the app it makes for a great refresher.
However i have one concern.
There is an old Chinese proverb that says.
I hear I forget
I see I remember
I do I understand.
Many of your things state what something does very well, but then only ask the participant to change a single value or variable rather than interact with the command being taught. This stood out to me in the loop example with the word grasshopper. Nothing said that it would take each letter in a string individually so i was wracking my brain trying to figure out how to break it down.
That was me just over thinking things. But the actual solution was type the word grasshopper. This shows a loop working but does not have you useing a loop.
Again, the app is great. But i feel in its current state it is more of a refresher tool than a teaching one.