With the nationwide closures of educational institutions in the United States due to the novel coronavirus disease 2019 (COVID-19), many schools transitioned from face-to-face instruction to eLearning formats at the beginning of the pandemic, while many students and their families self-isolated at home. The literature has revealed that self-isolation has a negative effect on adolescents' psychological outcomes, and high social support buffers against these outcomes. The purpose of the present research was to examine the moderating effect of perceived teacher support in the relationships between self-isolation during the beginning of the pandemic and negative health outcomes. Teacher support, self-isolation during the beginning of the COVID-19 pandemic, and health outcomes (i.e., suicidal ideation, nonsuicidal self-harm, subjective health complaints, depression) were measured in mid-April 2020 and health outcomes were measured again in late-May 2020. Participants were 467 7th and 8th graders (51% female; M[subscript age] = 13.47; ages range from 12 to 15 years old) from the suburbs of a large Midwestern city in the United States. The findings revealed that greater perceived teacher support buffered against the negative outcomes associated with self-isolation during the beginning of the COVID-19 pandemic and lower perceived teacher support strengthened these relationships. The results might inform policy development regarding strategies to improve health outcomes for adolescents during the COVID-19 crisis and future pandemics.