This study investigated the hypothesis that academic vocabulary instruction infused with morphological analysis of bound Latin roots--such as analysis of the relation between innovative and its bound root, nov (meaning "new")--will enhance word learning outcomes for English Learner (EL) adolescents. Latinate words with bound roots comprise a majority of general academic vocabulary words in English and are ubiquitous in texts across content areas. However, the effect of instruction in this area of morphology is unclear. Theory suggests that morphological knowledge is a critical component of lexical representations, binding a word's phonological, orthographic and semantic features. We hypothesized that instruction in bound Latin roots would (a) produce stronger outcomes for learning academic words by strengthening semantic and orthographic representations, and (b) equip students with morphological analysis skills to problem-solve new words. Employing a within-subjects design, 84 EL students participated in both of two counterbalanced conditions: vocabulary intervention without roots (comparison) and vocabulary intervention with roots (treatment). Effects on learning meanings of academic words were similar across conditions. However, the "with roots" condition showed large treatment effects for morphological problem-solving of unfamiliar words, and also suggested positive treatment effects on lexical access, lending partial support to our hypothesis that instruction about bound Latin roots contributes to EL adolescents' academic vocabulary learning. [This paper was published in "Reading and Writing" v32 n3 p689-727 2019 (EJ1208203).]