Assessing English learners (ELs) in US schools is challenging because many widely used assessments have not been designed with ELs in mind. Yet if teachers are sensitive to how ELs may perform differently from native speakers on such assessments, these assessments reveal useful information about ELs’ language and literacy skills. This mixedmethod study compared adolescent ELs’ performance on the Qualitative Reading Inventory-5 (QRI-5), Peabody Picture Vocabulary Test-4 (PPVT-4), and Words Their Way Elementary Spelling Inventory (ESI) to existing data from English-proficient examinees’ performance to explore how ELs’ performance may differ. The observed differences suggest that linguistic aspects of the QRI-5, PPVT-4, and ESI, including syntax, phonology, orthography, and especially vocabulary, played a role in ELs’ performance and indicate that ELs may benefit from linguistic modification or first-language support during test administration. The process used in this analysis also demonstrates how teachers can examine test data alongside test scores as they interpret ELs’ results.