How it works
The word appears one box per character, so a child can see exactly where they are.
The next key is not lit at first, because finding it is the lesson. It lights up after
three wrong keys for the same letter, or after ten seconds without a key, and when that
key needs shift, shift lights up too.
The keyboard is the whole one — number row, working shift, symbols above the digits.
Pressing shift visibly changes every key at once, which is the thing being taught. A
wrong key is refused and nothing already typed is lost.