This paper examines the degree of DIF detected on an English language proficiency assessment and the extent to which item characteristics may be identified as sources of DIF for Vietnamese- and Spanish-speaking students. Logistic regression was used to determine the extent of DIF for each item. Of the 45 items individually analyzed, 27 items were flagged for evidence of containing uniform or nonuniform DIF, the majority of which favored Vietnamese-speaking students. Effect sizes reflecting the magnitude of DIF for each item were correlated with item characteristics to determine the extent that item characteristics could explain variability in proficiency. Both multisyllabic words and unique-to-English sounds were significantly correlated with effect size, indicating these variables may partially explain the difference in item proficiency between language groups.