This study aimed to examine changes in depression and anxiety symptoms from before to during the first six months of the COVID-19 pandemic in a sample of 1,339 adolescents from three countries (9-18 years old, 59% female). We also examined if age, race/ethnicity, disease burden, or strictness of government restrictions moderated change in symptoms. Data from 12 longitudinal studies (10 U.S., 1 Netherlands, 1 Peru) were combined. Linear mixed effect models showed that depression symptoms increased significantly (median increase=28%), whereas anxiety symptoms remained stable overall. The most negative mental health impacts were reported by multiracial adolescents and those under ‘lockdown’ restrictions. Policy makers need to consider these impacts by investing in ways to support adolescents’ mental health during the pandemic.