Check & Connect, a mentoring intervention, has shown promise in promoting school engagement of students with disabilities; however, its social validity has not been examined in the literature. The absence of Check & Connect social validity data reflects the limitations of broader intervention literature and the area of social validity research. Therefore, the purpose of this study was to investigate social validity of Check & Connect and the influencing variables using existing data from the Center of Adolescent Research in Schools (CARS), a longitudinal, randomized controlled trial. A series of multiple regressions with multiple imputation was conducted. Results revealed that (a) students and mentors perceived Check & Connect as acceptable; (b) students' social validity ratings in Year 1, dosage across two-years, and change in mentor as a whole significantly explained 15% of the variance in students' Year 2 ratings, but only Year 1 ratings significantly predicted Year 2 ratings; (c) student and mentor characteristics (i.e., student behavior severity and special education status, and mentor years of teaching experience) were not significant in predicting students' and mentors' social validity ratings in Year 2; and (d) mentors' social validity ratings in Year 2 significantly predicted their treatment integrity in the same year despite the magnitude being small (10% of the variance). Implications for practice and future research pertaining to replication, assessment, methodology, and utility are discussed.