This study examined multilingual learners' achievement and growth in their language and literacy skills. Fifty-two multilingual students in Grades 2 and 4 with varying levels of English proficiency from Spanish-speaking homes in the American South participated in this study. They were assessed on English reading comprehension (RC), English word reading, and English-only, Spanish-only, and Spanish-English conceptually-scored vocabulary knowledge across a school year. Descriptive and a series of ANOVA analyses revealed that English learners' scores on all the measures were lower than those of their English-proficient multilingual learner peers. Further, students evidenced low-average English RC and English word reading, especially non-word decoding. Most importantly, multilingual students' performance on Spanish-English conceptually-scored vocabulary assessments revealed a positive pattern of achievement and growth, sharply contrasting with results based on typically-used English-only or Spanish-only monolingual vocabulary assessments. Practical assessment and instructional implications are discussed.