Number line estimation from kindergarten to grade 2: A longitudinal study

•Variability in estimation accuracy but not in evolution.•Arabic numerals have a more linear distribution than number words.•Number words dominant as format in grade 2.•Language explains variation in kindergarten but not evolution.•Untimed math learning can be predicted by estimation skills.

A bulk of evidence supports the association of number line estimations using Arabic digits and dots with math learning. Surprisingly few studies have been conducted to explore the relationship between estimations using number words and mathematics. The present study expands previous findings by investigating estimations in three formats (Arabic digits, dots and number), adding language as predictor and by focusing at timed and untimed math learning. A sample of 132 children was followed from kindergarten till grade 2. Results reveal variability in estimation accuracy and errors declining with age and instruction in all children. In addition, our findings suggest that Arabic numerals have a more linear distribution than number words. Moreover, our findings suggest that language explains variation in kindergarten but not in evolution and, more in particular, untimed math achievement can be predicted by number line estimation. Implications for assessment, prediction of math learning and instruction are discussed.