Why Does It Matter for Kids?

To adults, saying “this group has more than that one” sounds clear and obvious. But for kids aged 3 to 6, it’s anything but. The famous Swiss psychologist Jean Piaget showed that children think differently from adults — relying more on what they see than on logical reasoning. His classic experiments showed that kids can count two rows of objects and get the same number — but still say one row has more, just because it looks wider or takes up more space.

For example, if two rows of toy figures are lined up facing each other, a child might say, “There are the same number — it’s a fair match.” But if one row is spaced out to look longer, the child may decide that this side has more — and is now likely to “win.” Even counting and finding the same total in both rows doesn’t convince the child that nothing has changed.

This shows us that understanding quantity isn’t something kids are born with. It develops gradually, through real-world actions — like setting a spoon next to every bowl, putting hats on dolls, or giving toy animals a place to sit. In activities like these, kids make an important discovery: items from two groups can be paired up one-to-one, and this lets them see whether the groups are equal or if one has more or less.

Research by American psychologists confirms that the ability to make one-to-one matches is linked not only to early math thinking, but also to general logical reasoning and an understanding of conservation of number — the idea that the number of items stays the same regardless of how they’re arranged. Learning to compare groups through one-to-one correspondence is a key milestone in developing number sense. Studies show that kids begin shifting from visual judgment to formal number logic only when they understand that the order in which objects are counted doesn’t change the total.

This skill is also strongly connected to later success in arithmetic. Kids who confidently apply one-to-one correspondence tend to develop a better understanding of addition and subtraction. A major longitudinal study by the U.S. National Institute of Child Health found that even by third grade, differences in kids’ ability to mentally compare groups of objects were still strongly related to their performance in both math and logic.

In other words, when kids play games like “who has more?”, “who didn’t get enough?”, or “who was left without a chair?”, they’re not just learning to count — they’re learning to reason about numbers and quantities.