Boarding school has been a feature of education systems for centuries. Minimal large-scale quantitative data have been collected to examine its association with important educational and other outcomes. The present study represents one of the largest studies into boarding school conducted to date. It investigates boarding school and students’ motivation, engagement, and psychological well-being (e.g., life satisfaction, interpersonal relationships)—controlling for sociodemographic, achievement, personality, and school covariates. The main sample comprised 5,276 high school students (28% boarding students; 72% day students) from 12 high schools in Australia. A subsample of 2,002 students (30% boarding students; 70% day students) had pretest data, enabling analyses of gains or declines in outcomes across the school year. Results indicated predominant parity between boarding and day students on most outcome factors, some modest positive results favoring boarding students, and no notable differences in gains or declines on outcomes between boarders and day students over the course of one academic year. Implications for researchers, the boarding sector, parents, and students are discussed.