As the COVID-19 (SARS-CoV-2) virus spread across the world, countries took drastic measures to counter the disease by requiring their citizens to home self-isolate i.e., lockdown. While it was not known how young people would cope with the social distancing restrictions, there was concern that the lockdown would have a debilitating effect on youth mental health. This study examined whether there was an association between adolescent subjective wellbeing and the amount of time spent in lockdown. Global Research Alliance researchers in 15 countries collected data using the Mental Health Continuum (Keyes in Am J Orthopsych 76:395–402, 2006) from over 7000 middle-school students aged 11–18. Findings show a decline in eudemonic wellbeing, particularly among females during the first 6 months of lockdown, which was most strongly associated with diminished psychological wellbeing, followed by social wellbeing, while emotional wellbeing remained relatively stable. An adaptation effect was noted after approximately 6 months. There was evidence suggesting females were slower to adapt to lockdown conditions compared to males. More attention should be paid to the wellbeing of students in lockdown to overcome languishing tendencies and educators should be cognizant of diminished student wellbeing, particularly among females, when students return to school. Positive school experiences, and positive relationships within the school community, may assist in reducing the risk of languishing in lockdown conditions, so schools should design interactive online activities for off-campus learning.