The Academic Intrinsic Motivation Scale (AIMS) measures key components of student intrinsic motivation (IM). We investigate score validity and reliability of a downward extension of the AIMS developed for students in the high school context using a sample of students from the Pacific Northwest region of the United States. Through classical test theory, this study documents the scale's (1) item difficulty and discrimination, (2) underlying factor structure and score reliability via confirmatory factor analysis and omega coefficients, and (3) relationship with the theoretically related variables student retention, achievement, and teamwork ability. Findings support scoring, generalizability, and extrapolation inferences for the downward extension of the AIMS in a high school sample. Implications for additional psychometric validity evidence are discussed.