Approximate number word knowledge before the cardinal principle

• We examine approximate number word knowledge among 3-5-year-olds.
• Some children use numbers approximately before learning the cardinal principle.
• Child age, but not knower-level, significantly predicts approximation ability.
• Older children’s verbal estimates are more likely to distinguish set sizes 5 to 10.

Approximate number word knowledge—understanding the relation between the count words and the approximate magnitudes of sets—is a critical piece of knowledge that predicts later math achievement. However, researchers disagree about when children first show evidence of approximate number word knowledge—before, or only after, they have learned the cardinal principle. In two studies, children who had not yet learned the cardinal principle (subset-knowers) produced sets in response to number words (verbal comprehension task) and produced number words in response to set sizes (verbal production task). As evidence of approximate number word knowledge, we examined whether children’s numerical responses increased with increasing numerosity of the stimulus. In Study 1, subset-knowers (ages 3.0–4.2 years) showed approximate number word knowledge above their knower-level on both tasks, but this effect did not extend to numbers above 4. In Study 2, we collected data from a broader age range of subset-knowers (ages 3.1–5.6 years). In this sample, children showed approximate number word knowledge on the verbal production task even when only examining set sizes above 4. Across studies, children’s age predicted approximate number word knowledge (above 4) on the verbal production task when controlling for their knower-level, study (1 or 2), and parents’ education, none of which predicted approximation ability. Thus, children can develop approximate knowledge of number words up to 10 before learning the cardinal principle. Furthermore, approximate number word knowledge increases with age and might not be closely related to the development of exact number word knowledge.