As the school-aged English language learner (ELL) population continues to grow in the United States and other English-speaking countries, psychometrically sound instruments to measure their language learning strategies (LLS) become ever more critical. This study adapted and validated an adult-oriented measure of LLS (50-item Strategy Inventory for Language Learning [SILL]; Oxford, 1990) for school-aged ELLs in a sample of 1,057 elementary, middle, and high school students. The two-stage validation process resulted in a shorter, 28-item version of the instrument, which we entitled the SILL–ELL Student Form. The results of confirmatory factor analyses indicated a good fit to the validation (GFI = .92, CFI = .93, RMSEA = .04, SRMR = .05) and combined (GFI = .95, CFI = .95, RMSEA = .03, SRMR = .04) samples. The new measure has strong psychometric characteristics for use with school-aged ELLs to diagnose their use of LLS in six distinct categories and is approximately half as long as the original SILL, which enhances its pragmatic value for busy classrooms. Additionally, this study addressed some of the theoretical issues with strategy categorization noted in the literature. Other applications of the measure for practice and research are discussed.