My heir has lots of stuff that is supposed to teach him how to count – these little cards are just one example. All those study aids, however, are overestimating the human perception quite a bit: while it is immediately obvious how many items are on the 1, 2 or 3 cards, may be on the 4 one, but certainly not on the 8, 9, 10 ones. In order to figure out how many items are there I have to count them and if I can’t count… well, there a catch-22 right there!
What one needs to learn is really just the order: 1 < 2 < 3 < 4 < … < 10 and so on, so one would think the study aid should emphasize that – say, by showing exactly the same items as on the smaller number card, with exact same disposition and adding one extra item to show that this number is one step larger than the previous one. But no, designers get so carried away with drawing cute items of various kinds in various groups that those illustrations become useless.
I saw these “helpful” drawings go all the way up to 20(!) in one book. Well, here’s one more useful picture: