Vocabulary represents a key barrier to language and literacy development for many English learners. This study examined the relationship between Spanish-speaking English learners’ conceptually scored Spanish–English vocabulary, academic English proficiency, and English reading comprehension. Second- and fourth-grade English learners (N = 62) completed standardized conceptually scored vocabulary measures in the fall and state-administered standardized measures of academic English proficiency and English reading comprehension in the spring. Conceptually scored vocabulary measures are designed to tap knowledge of the number of known concepts, regardless of the specific language (Spanish or English) used to label the concept. Regression analyses revealed that academic English proficiency and English reading comprehension were not predicted by the conceptually scored measure of receptive vocabulary. However, both academic English proficiency and English reading comprehension were predicted by the conceptually scored measure of expressive vocabulary. In addition, the relationship between conceptually scored expressive vocabulary and English reading comprehension remained after controlling for academic English proficiency. Results underscore the utility of measures that incorporate English learners’ first and second language skills in understanding the vocabulary knowledge English learners bring to English language and literacy learning tasks.