Despite the importance of cognitive development for vocabulary acquisition, limited attention has been given to the impacts of cognitive factors on this phenomenon from a longitudinal perspective. This study evaluates the longitudinal development of such factors (i.e. metacognitive knowledge, working memory, and non-verbal intelligence) and L2 vocabulary knowledge growth in 210 young second language learners enrolled in a bilingual programme in China. Results supported individual differences in the initial level and the growth rate of learners’ cognitive development and vocabulary knowledge growth: a higher starting level of cognitive development correlated with a higher level of vocabulary knowledge and a faster rate of vocabulary knowledge growth. Findings revealed particularly significant predictive role of metacognitive knowledge on vocabulary knowledge, followed by non-verbal intelligence and working memory. Relevant implications were discussed based on the findings.
