This quasi-experimental study used a pre-test-post-test control group to assess the effectiveness of a locus of control-based smoking prevention program designed for secondary school students. The study included 204 children, 103 in the intervention group and 101 in the control group, who were in fifth grade at two secondary schools in İzmir, Turkey. The control group in the study received standard education and training, whereas the intervention group received a locus of control-based smoking prevention program for 14 weeks. The Data Collection Form, the Nowicki-Strickland Internal-External Locus of Control Scale, the Problem-Solving Inventory for Children, the Middle School Self-Efficacy Scale, and the Decision Balance Scale were used to collect research data in the third, sixth, and twelfth months following the training. The data was evaluated using multi-way and one-way analysis of variance for repeated measures, Bonferroni corrected t-test, ANCOVA and effect size, and the chi-square test for power analysis. The relationship between the training program and the study's other sub-dimensions was explained using structural equation modeling. It has been determined that the developed model effectively alters cigarette trial scenarios. The intervention and control groups differed significantly in their impression of smoking advantages (p<0.05), but there was no significant difference in time or group*time interaction (p>0.05). There was a change in perception of smoking hazards over time (p<0.05), but no significant difference was detected in terms of group or group*time interaction (p>0.05). The mean self-efficacy scores differed by group and time (p<0.05), but there was no significant difference in group*time interaction (p>0.05). The intervention and control groups showed significant differences in mean scores for locus of control and problem-solving skills across time, group, and group*time interactions (p<0.05). There was no difference between the smoking trial statuses. The intervention program was shown to have a minor effect size and borderline power for smoking. As a result, it was determined that the locus of control-based smoking prevention program had little influence on improving children's locus of control, self-efficacy, problem-solving scale mean scores, and perceptions of smoking harms while decreasing perceptions of smoking advantages. Additionally, it was revealed that the intervention approach was ineffective in stopping children from smoking.