What it teaches
Typing anything, not just words. The rungs go small letters, a capital at the front, letters with numbers, one symbol, then all of it at once. By the fifth a child can type anything a grown-up is ever asked to type — which is the point, because the first thing they will be asked for is a password.
Shift is the real lesson. It is the first key a child meets that changes what the other keys do, and nobody explains it: they are told "hold shift for a capital" and left to find the rest by accident.
What to look for
Correct fingers do not matter yet. Finding the keys does, and a child who has to hunt for every one cannot write anything longer than a word.
On the strict settings the next key is not lit. That turns this into a test, which is the right thing for a child who has already done the first three rungs easily.