This study tested the efficacy of a school-based prevention program for reducing suicide potential among high-risk youth. A sample of 105 youth at suicide risk participated in a three-group, repeated-measures, intervention study. Participants in (1) an assessment plus 1-semester experimental program, (2) an assessment plus 2-semester experimental program, and (3) an assessment-only group were compared, using data from preintervention, 5-month, and 10-month follow-up assessments. All groups showed decreased suicide risk behaviors, depression, hopelessness, stress, and anger; all groups also reported increased self-esteem and network social support. Increased personal control was observed only in the experimental groups, and not in the assessment-only control group. The potential efficacy of the experimental school-based prevention program was demonstrated. The necessary and sufficient strategies for suicide prevention, however, need further study as the assessment-only group, who received limited prevention elements, showed improvements similar to those of the experimental groups.