What it teaches
Alphabetical order applied to letters that are not next to each other. Knowing the alphabet by heart and being able to say that P comes before S are not the same thing, and the second is the one that gets used.
How it works
A handful of letters appear out of order and are dragged into place. The number grows as the rounds go on, from three up to ten.
Dragging is forgiving on purpose: the drop counts when the tile is near a slot rather than exactly over it, because a seven-year-old's hand is not steady and the game is not testing that.
What to look for
At the larger sizes children usually stop reciting the alphabet from A and start comparing pairs. That change is worth noticing — it is the moment the knowledge became usable.