Background: Chile's national school-based mental health program, "Skills for Life" (SFL), has demonstrated effectiveness in improving behavioral and academic outcomes in first- through third-grade students. The current study assessed the feasibility and outcomes of SFL's program for sixth- through eighth-grade students. Methods: We assessed the percentage of students who participated in the program and longitudinal changes on teacher-reported Teacher Observation of Classroom Adaptation Re-Revised (TOCA-RR) scores, youth-reported Pediatric Symptom Checklist-Chile (PSC-Y-CL) scores, grade-point average, and school attendance from sixth to eighth grade (2016-2018) for SFL's workshop intervention. Linear mixed effects models analyzed the association between outcome variables and workshop attendance. Results: Of the 30,649 sixth graders who attended the 754 participating schools in 2016, 28,204 (92.0%) were screened with the TOCA-RR. Of the 1829 students who screened at risk, 1344 had available workshop data for seventh grade, with 86.9% of them participating in most ([greater than or equal to] 7) workshop sessions. Workshop attendance was significantly associated with improvements in school attendance and peer relationships (a TOCA-RR subscale) in eighth grade. Conclusions: With high rates of behavioral health screening and workshop attendance, this study demonstrated the feasibility of implementing SFL's middle school program on a national scale. Higher workshop attendance by at-risk students was associated with better school attendance and peer relationships in eighth grade, as well as better but not significantly different outcomes on other measures (e.g., teacher-rated school performance and aggressive behavior in the classroom). Overall, these findings provide preliminary evidence of the feasibility and benefits of SFL's middle school program.