Does mathematical vocabulary predict the change in students' performance on mathematical tasks from one academic year to the next? Chilean Spanish-speaking students (N = 87) completed measures of mathematical vocabulary, mathematical skills (i.e., arithmetic fluency, calculation, and applied problems), receptive vocabulary, and working memory in Grade 2 (T1, Mage = 7:11 years:months, SD = 0:5, 46% girls). One year later (T2) they completed the same mathematical measures. Concurrent relations were found between mathematical vocabulary and the three mathematical skills at both time points. Together, general and mathematical vocabulary at T1 explained significant unique variance in the change in applied problems and calculation from T1 to T2. For calculation however, only mathematical vocabulary predicted significant unique variance in the change from T1 to T2. Change in arithmetic fluency was only predicted by working memory. These results address the roles of general and mathematical vocabulary in students' mathematical development in elementary school.