This study addresses the associations between students’ ability beliefs and attitudes toward inclusion in physical education, as well as the impact of gender and previous contact/participation with children with disability on these variables. A cross-sectional study was conducted with 976 students (491 girls and 485 boys; age 11–16 years), who responded to ability beliefs and attitudes questionnaires. Ability beliefs (entity and incremental) and the 3 sociodemographic variables predicted 20.4% and 9% of the behavioral and cognitive subscales of attitudes, respectively. Students with higher scores for entity beliefs of ability had a less favorable attitude toward inclusion. Girls reported more favorable attitudes toward inclusion than boys. Students who indicated previous participation in physical activities with children with disabilities showed attitudes that were more favorable in both the behavioral and cognitive subscales, while those who reported previous contact had more favorable attitudes in the behavioral subscale and lower entity beliefs. However, the 3 sociodemographic variables had a lower contribution to the explained variance of attitudes.