In this study, researchers evaluated the effects of peer-assisted multimedia vocabulary instruction, which was designed to address the goal of building knowledge of discipline-specific definitions of language arts terminology for six ninth-grade English Language Learners (ELLs) with or at-risk for learning disabilities. To evaluate the effects of the intervention on the accuracy and completeness of students' expressive definitions, researchers used a multiple probe design replicated across word sets and participants. Instruction took place in 20-minute sessions that spanned 29 consecutive school days. After the intervention, all six students increased the number of accurate expressive definitions and self-evaluated higher levels of word knowledge (i.e. "I know it and can give an example" or "I can teach this word to someone else"), respective to their baseline performance levels. The pattern of improvement on expressive definitions tests was replicated across word sets and participants, suggesting the overall effectiveness of the intervention on the acquisition of discipline-specific definitions of language arts terms. In addition, students reported high levels of satisfaction with the intervention's procedures and outcomes.