What it teaches
Choosing between ą and ę. Unlike ó and u these two do not sound the same, but they swap inside a word family — ząb and zęby, dąb and dęby, gęś and gąski — and a child who reaches for the related word gets most of them right without remembering any of them.
The endings are the other reliable group: an infinitive ending in -ąć takes ą every time.
How it works
A word with a gap and two letters, the same shape as the other three spelling games. The related word is shown as the hint, so what arrives is the rule rather than the answer.
Three levels. The first two use the plain words; the third brings in the exceptions and the words where the rule only works if you already know another word. An exception is worth meeting once the rule it breaks is known, not before.
What to look for
Say the related word out loud together — "ząb, and more than one is?" — and let the child hear the swap. It works far better than the written hint.
Ą before ć is the one worth drilling separately: wziąć, zacząć, zdjąć. That group is small and it is on level three.