Developmental change in number line estimation: A strategy-based perspective.

The current study investigated developmental changes in children's benchmark-based strategy use in number line estimation. Third and fifth graders solved a 0-1,000 number line estimation task in one of three conditions. In the control condition, only the origin and endpoint were specified, the midpoint condition included an additional benchmark at 50%, and the quartile condition contained three additional benchmarks at 25%, 50%, and 75%. Trial-by-trial verbal strategy reports revealed that fifth graders, in comparison to third graders, spontaneously applied quartile-based strategies more frequently while they used strategies based on the origin, midpoint, and endpoint about equally often. Finally, children's mathematics achievement was positively related to the variety and frequency of benchmark-based strategies as well as their number line estimation performance. We conclude that developmental changes in number line estimation performance can at least partially be attributed by a refinement in children's benchmark-based strategy use.