English language learners (ELLs) constitute one of the fastest growing subpopulations of students in the United States. It is important to determine whether the assessments used by states in determining students' proficiencies are valid and fair for ELLs. This study focused on several standards-based assessments in mathematics and science administered to 5th and 8th graders. In assessing construct validity, all of the assessments were found to be essentially unidimensional in their underlying factor structure for native English speakers and for several ELL examinee groups. The use of translation glossaries/word lists as a testing accommodation was effective for supporting the unidimensionality of some of these assessments, specifically for the one at the 8th-grade level. (Contains 15 tables and 2 figures.)