How natural disasters affect the psychological state of adolescents has not been well studied. Thus, we examined the effect of a natural disaster on high-school-aged youth and considered the most effective forms of support following such a disaster. We examined students from two high schools that were near the epicenter of the 9.0-magnitude Great East Japan Earthquake, which struck the Tohoku coastal area on March 11, 2011, causing severe damage to the region. The questionnaires measuring depression, anxiety, and post-traumatic stress reaction (PTSR) was administered to the students 3 times between July 2012 and August 2014; students who scored above the cut-off values of these measures were considered highrisk students. School teachers, nurses, and counselors provided a school-based intervention for all highrisk students identified in the survey. Data were analyzed using the Kruskal-Wallis H-test. Survey data revealed that 860 of the 1,432 (55.9%) high school students were at high risk of psychological trauma in 2012. This rate did not change substantially in the following 2 years, reaching 1,059 of 1,488 (69.1%) in 2013, and 949 of 1,430 (62.7%) in 2014. Depression and PTSR scores were significantly lower after the intervention (for 2nd and 3rd grade students in 2013 and 2014) compared to before (for the initial 2012 survey). However, there were no significant differences between the 1st grade students for all three years. Thus, school-based interventions involving psychological testing and interviews might reduce the rates of depression and PTSR in high school students.