This study aims to understand the role that reading motivation plays in middle school reading achievement (including achievement gaps) by analyzing the 2015 grade 8 NAEP reading data. The study focuses on identifying the unique effects of student-level reading motivation and aggregated school-level mean reading motivation on reading achievement. Hierarchical linear modeling is used to partition variability in student reading achievement into within- and between-school components after student- and school-level demographic variables are taken into account. In addition, this study investigates whether the identified unique effects of reading motivation on reading achievement vary by gender, race/ethnicity, English language learner status (ELL), and other demographic variables. Finally, the study examines the roles that students' demographic characteristics and reading motivation play in understanding reading achievement gaps based on students' race/ethnicity and ELL status Results show that student reading motivation is substantially associated with student reading achievement, even after taking into account student gender, race/ethnicity, and SES, ELL, IEP statuses, and interaction terms, which comports with the literature on the effects of reading motivation on reading achievement. In addition, the study identifies the unique and substantial effect of school-level mean motivation on school mean reading achievement even in the presence of other school demographic variables, which highlights the significant role schools might have on promoting students' academic development.