Preventative interventions for depression in high school students are often targeted to cognitive-behavioral factors, such as maladaptive cogitation, inadequate social skills, or rumination. Although previous research has revealed that cognitive-behavioral factors are important for reducing depression, there is little evidence regarding the factors that most effectively predict increased depression in high school students. Therefore, we sought to identify the most predictable long-term cognitive-behavioral factors in depression by comparing these three factors. We conducted a 1-year two-wave longitudinal questionnaire survey with 51 high school students. The results revealed that only rumination predicted depression after 1 year, but the predictive effect was relatively small. Moreover, maladaptive cognition and social skills, which are usually targeted by prevention intervention, did not account for increased depression. The current findings suggest that it would be valuable for future studies to further clarify which factors affect depression among high school students.