The purpose of this article is to explore the use of reading aloud and maze Curriculum-Based Measures (CBMs) to evaluate the responsiveness of secondary-level English language learners (ELLs) to peer-mediated instruction. First, we briefly summarize research on instructional practices for ELLs, highlighting the need for further work to identify scientifically based assessment and interventions for diverse learners. Second, we review research on Peer-Assisted Learning Strategies for general classroom use as well as for use with ELLs. Third, we review research on CBM, including evidence supporting its use with ELLs. Finally, we illustrate how CBM can be used to evaluate ELLs' responsiveness to PALS, using case examples drawn from a study of PALS for secondary-level ELLs. We discuss factors to consider when assessing ELLs' responsiveness to scientifically based instruction and directions for future research.