Twenty years ago few preschools (or parents, for that matter), paid much attention to teaching mathematics to four-year-olds. In 1998, for example, only four percent of a nationally representative sample of American children entering kindergarten could add or subtract. Today, math is firmly entrenched in the pre-K curriculum. And the Common Core State Standards, which are the new instructional guidelines for K-12 math instruction in 40+ states, and which require kindergartners to engage in algebraic thinking, are being extended downward into pre-K in many locales. New York state, for example, has pre-K standards aligned to the Common Core that require four-year-olds to “demonstrate an understanding of addition and subtraction by using objects, fingers, and responding to practical situations (e.g., If we have three apples and add two more, how many apples do we have all together?).” Thus, in about 15 years we’ve moved from virtually no preschoolers being able to add and subtract to the goal of all four-year-olds being able to do so.
There is a scientific basis for the growth in the emphasis on math in pre-K, as researchers in early mathematics have followed previous work by early literacy researchers by investigating the longitudinal associations between early skills and later development. As a result of these efforts, we now know that early math skills are the strongest early predictors of children’s math achievement years later (Aunola, Leskinen, Lerkkanen, and Nurmi, 2004; Duncan et al., 2007; Geary, Hoard, Nugent, and Bailey, 2013; Jordan, Kaplan, Ramineni, and Locuniak, 2009; Siegler et al., 2012). This finding, in turn, provides an empirical basis for devoting a considerable chunk of the pre-K curriculum to math instruction, since math skills and course taking during the high school years are related to important life outcomes such as college success (Lee, 2013). Unfortunately, the effects of early math interventions found in experimental studies clearly diminish over time. My recent work suggests that differences in children’s math achievement are influenced by a combination of differences in both earlier math achievement and the relatively stable factors affecting children’s math achievement across development— with the effects of stable factors being several times larger than the effects of children’s earlier math achievement. This suggests that pre-school level math instruction alone will not be sufficient to substantially boost long-term math achievement outcomes, and raises important questions about what kinds of interventions are likely to produce the longest lasting effects on children’s math achievement.
Examining the relation between early and late mathematics skills
The strong association between children’s measured math skills in preschool and later, during the school years, is only a warrant for an emphasis on math instruction in pre-K if the relationship between earlier and later skills is causal, e.g., teaching children to add and subtract as four-year-olds leads directly to increased math learning for those children in elementary school. If the correlation between early and later math skills is fully driven by other variables that affect both early and later math skills, such as children’s intelligence or interest in learning, then teaching preschoolers to add and subtract would not have a direct impact on later math skills.
Researchers have tried to rule out other variables that might explain the correlation between earlier and later mathematics ability by controlling statistically for some of the factors that might affect children’s math learning both early and later in their development, including: family characteristics; children’s cognitive abilities such as intelligence and working memory; and reading achievement. These statistical controls are used to reduce bias in the estimates of the effect of early math achievement on later math achievement.
To the extent that we are able to make causal inferences from these studies, the implication is clear: improving children’s early math skills should produce sizable effects on their much later math achievement. This would be good news, as we know of some effective ways to increase children’s math achievement in preschool; for example, Doug Clements’s and Julie Sarama’s early math curriculum produces impressive effects on children’s early math achievement (Clements, Sarama, Spitler, Lange, and Wolfe, 2011; Clements and Sarama, 2008).
Further, there is a promising logic underlying the idea that effective early math interventions will have long-lasting effects. In math, earlier skills are often repurposed as subroutines of later skills. For example, children use counting when they learn single digit arithmetic, they use single digit arithmetic when they learn multi-digit arithmetic, and they use whole number arithmetic when they learn fraction arithmetic. Failing to learn earlier skills disadvantages children trying to