Remembering numbers is one of the most basic things we do from a young age - early on, a combination lock or a phone number and later any number of things such as ATM codes, social security numbers, and more.

In Western cultures, children learn to place numbers on a mental number line - smaller numbers to the left and spaced further apart than the larger numbers on the right. Then the number line changes to become more linear, with small and large numbers the same distance apart. Children whose number line has made this change are better at remembering numbers, according to a new study published in Psychological Science.

For the study, Clarissa A. Thompson of the University of Oklahoma and Robert S. Siegler of Carnegie Mellon University looked at how children's memory for numbers relates to the way they represent numbers in their heads.    

In one experiment, each child was given a stack of blank number lines, with "0" written below the left end and "20" written below the right end. Then the child heard a series of numbers from 1 through 19 and had to mark on each number line where they thought that number belonged. Then the experimenter told a story that included a few numbers. The child was asked to name four cartoon characters, to throw off their memory a bit. (Thomas the Tank Engine and Dora the Explorer were favorites.) After that, the experimenter asked questions about the story, like "How many forks did Colleen wash?" Children with a more linear number line were better at remembering the numbers in the story.

"Young children's knowledge sometimes seems impressive, because they can count, 'one two three four five six seven eight nine ten,' but often they just learn by rote. Their counting doesn't have much to do with their understanding of how big the numbers are," says Thompson. But eventually these words get associated with the size of the numbers. Children normally start out with a logarithmic number line, which has more space between smaller numbers and crunches the larger numbers together at the top. Eventually they progress to a linear number line.

In three experiments, Thompson and Siegler found that the more linear a child's number line, the better the child was at remembering numbers. This was true for preschoolers for numbers from 1-20 and for elementary school children for numbers from 1-1000. "We really do live in a world of numbers," says Thompson. "Some we only need to approximate, and others we need to remember exactly. Ability to estimate the sizes of numbers influences the ability to remember the numbers exactly."

Citation: Clarissa A. Thompson, Robert S. Siegler, 'Linear Numerical-Magnitude Representations Aid Children’s Memory for Numbers', Psychological Science, Published online before print July 19, 2010, doi: 10.1177/0956797610378309