Youth suicides have diverse characteristics according to the young people's developmental stages. Warning signs and communication of suicidal intent can be vague among early adolescents, while mental health problems may be more evidently related to suicidal ideation in older adolescents. Understanding the developmental characteristics of youth suicide is necessary for effective suicide prevention. We explored the differences between children and adolescents who died by suicide and the characteristics of these young people as observed by their school teachers. We analyzed teachers' mandatory postmortem reports of suicides among 308 Korean students. We compared: suicide-related information including personal, familial, and school factors; stressful life events; and participation in interventions among elementary, middle, and high school students who died by suicide. We also assessed the distribution of student suicides per month. Suicide among elementary school students increased during school vacations, and suicide among middle and high school students increased during the school semester. According to the teachers' reports, elementary school students who died by suicide were more extroverted and had better academic achievements than their high school peers, and had significantly lower levels of substance/tobacco use. Elementary school students who died by suicide showed significantly less academic stress and use of external professional help than did other groups. Because this research is based on mandatory teacher reports, the subjective opinions of teachers may have affected the reliability of the data. Suicide by out-of-school youth was not included. School-based suicide prevention should be implemented in accordance with young people's developmental characteristics.