What is the significance of the School Strike for Climate from an international constitutional perspective? In this article, I compare the School Strike for Climate with the Hong Kong protests of 2019–20. Both these movements became necessary because of gaps in their countries’ respective domestic and international legal frameworks – what I term constitutionalism gaps. The immediate cause of each protest was how state and non-state actors exploited these constitutionalism gaps in the existing legal framework. Protests in Hong Kong were triggered by the attempt to enact an Extradition Law that threatened people’s autonomy, whereas the School Strike for Climate is a response to the failure of the state to deliver climate justice. Both these movements use similar strategies of advocacy and they have relied extensively on new technology. Based on this comparison, I argue that the School Strike for Climate promotes procedural and substantive values of constitutionalism at the international level, similar to the Hong Kong Protests at the domestic level. Through the School Strike for Climate, people seek to engage directly in the transnational legal process. In attempting to bridge the constitutionalism gap at the international level, the School Strike for Climate promotes values of global constitutionalism.