Many students still have not developed a robust understanding of
rational number concepts at the end of primary school, despite several
years of instruction on the topic. The present study aims to examine the
patterns, predictors, and outcomes of the development of rational
number knowledge in lower secondary school. Latent transition analysis
revealed that rational number development from primary to lower
secondary school (N = 362) appears to follow similar patterns as in
younger students. In particular, a majority of students had poor
knowledge of the density of the rational number set. Whole number
magnitude knowledge appeared to be an important predictor of the
development of rational number size knowledge, but not density
knowledge. Finally, fraction density knowledge appeared to be related to
concurrent algebra knowledge. Together these results point to an
important role for density knowledge in mathematical development.