Nonsuicidal self-injury (NSSI) and suicidality are common among adolescents. School staff are often the first adults to be confronted with those behaviors. However, previous studies have shown a lack of knowledge and confidence in dealing with self-harming behaviors. Objectives of this study were to evaluate a workshop on NSSI and suicidality in adolescence for teachers, school social workers and school psychologists. In total, N = 267 school staff participated in 1 of 16 two-day workshops, which were offered in different cities in southern Germany. Pre-, post- and 6-month follow-up assessments were conducted concerning attitudes, confidence in own skills, perceived knowledge, and knowledge on NSSI and suicidality. Satisfaction with the workshop was evaluated directly after the workshop; changes in handling situations involving youth with self-harm were evaluated at follow-up. Overall, participants were very satisfied with the workshop. Few negative attitudes regarding NSSI and suicidality were prevalent before and after the workshop. Large effect sizes were found for improvement in confidence, perceived knowledge, and knowledge at postassessment, which were still present at 6-month follow-up. There were significant differences between professions, with teachers seemingly benefitting the most from the workshop. At follow-up, participants reported more changes in their own behavior than having been able to implement changes on a school level. A 2-day workshop seems to be effective in changing knowledge and confidence in school staff regarding NSSI and suicidality. Workshops catered to different professions (i.e., teachers and school psychologists) might be feasible.