Ordinal skills influence the transition in number line strategies for children in Grades 1 and 2.

How do children place numbers on a line where only the endpoints are marked? Previous researchers have shown that the differential estimation patterns on the number line task reflect different strategies used by children. What factors influence their transition from less efficient to more efficient strategies? Children in Grade 1 (n = 66) and Grade 2 (n = 80) completed a 0-100 number line task at two time points of the school year. Their ordinal skills (i.e., number ordering) and spatial skills (i.e., mental rotation) were also measured. A latent transition analysis revealed two types of profiles. Children showing a variable profile were more accurate at estimating the numbers that are close to the endpoints and the middle of the line than other numbers, and their performance did not fit any of the linear, exponential, or logarithmic functions. In contrast, children showing a uniform profile were accurate across all target numbers (i.e., linear performance). Children's verbal strategy reports provided support for the latent profile classification; children showing a uniform profile were more likely to use relational strategies, suggesting they were considering the number line as a whole, whereas children showing a variable profile were more likely to count from one of the three common reference points (i.e., endpoints or the imagined midpoint). Transition between the variable and uniform profiles was predicted by children's ordinal skills, suggesting that children need to understand the ordinal associations among numbers to refine their solution strategies on the number line task.