What it teaches
What the three end marks mean: a full stop tells, a question mark asks, an exclamation mark shouts or orders. A child who can hear the difference in speech can usually choose correctly, and the game is mostly about connecting the two.
The third level moves to commas, which Polish is far stricter about than English. A comma before że and before który is compulsory, and there is no comma before i in a list. Those three rules cover most of what a primary school child writes.
How it works
The sentence appears with a space where the mark should be, and the three marks stay in the same order every time so that a child hunts for the rule rather than the button.
At level three the question changes: two whole sentences, one with the comma in the right place and one without, and the rule appears underneath.
What to look for
Read the sentence out loud with the child before they choose. The end mark is a question about the voice, not about the words, and hearing it makes the choice obvious.