Vocabulary Knowledge and Speaking Proficiency among Second Language Learners from Novice to Intermediate Levels

To remedy the paucity of studies on the relationship between vocabulary knowledge and speaking proficiency, we examine the degree to which second language (L2) speaking proficiency can be predicted by the size, depth, and speed of L2 vocabulary among novice to intermediate Japanese learners of English. Studies 1 and 2 administered vocabulary tests and a speaking test to 224 and 87 L2 learners, respectively. Analyses using structural equation modeling demonstrated that a substantial proportion of variance in speaking proficiency can be explained by vocabulary knowledge, size, depth, and speed. These results suggest the centrality of vocabulary knowledge to speaking proficiency.