Two types of assessment instruments were developed to assess middle school students' learning strategies, and their effectiveness in predicting various learning outcomes was examined. The participants were 565 middle school students. Three subscales (rehearsal, organization, elaboration) from the "Motivated Strategies for Learning Questionnaire" (Pintrich et al. 1991) formed a unique Learning Strategy scale. Memorization strategies (rehearsal and organization) were assessed with a specific learning task (memorizing word list). Math and language skills, assessed in Grade 7 and Grade 8, were used as outcome measures. The reported use of learning strategies, measured by Learning Strategy scale, was not related to any learning outcomes. In contrast, students who used memorization or organization during learning task differed in all outcomes. Results indicate a serious need to consider which assessment methods will be used in middle school. In the future, self-report questionnaires could benefit from subject-specific and more concrete descriptions of tasks. Meanwhile, we advise using questionnaire and cognitive behavioral learning task methods concurrently to assess learning strategies of middle school students.