Background: High school students, particularly in Japan, suffer from severe depression. School-based cognitive-behavioral depression prevention interventions are effective countermeasures against depression among high school students. However, due to the time-consuming nature of high school curriculum, such interventions are less common among high school students than they are among elementary and junior high school students, making it difficult to introduce them to a sustainable school curriculum. We used a long-term but low-frequency intervention as one of the implementation approaches to address curricular issues, which divide the program’s content across several grades. Therefore, this study examined the effectiveness of our approach to high school students.
Methods: We conducted the program on a grade-by-grade basis for students who entered the school each year over a two-year period. We administered surveys during the two-year intervention period and one-year follow-up period to 225 students who had enrolled in a high school during 2014–2019. Only those high schools were considered that implemented our program. Additionally, data from 608 Japanese high school students who did not receive this program were obtained through an online survey and compared to our data for higher levels of depressive symptoms at each grade level.
Results: According to the three-level hierarchical linear model analysis, students who participated in the program experienced improvement in their depressive symptoms and related factors over these three years. At the end of the program and one year after the intervention, the Welch test and chi-square test indicated fewer depressive symptoms and a lower percentage of students with depression compared to those who did not receive the intervention.
Conclusions: The results of this study suggest that a school-based cognitive-behavioral depression prevention program using a long-term but low-frequency approach may effectively reduce the implementation burden into the school curriculum, promote sustained implementation, and prevent depression among high school students. Future studies may consider other innovative methods to examine sustained intervention effects, considering economic and ethical issues, such as collecting depression scores of general high school students annually.