This article discusses three problems that need to be tackled when the climate crisis becomes 'a sustainability issue' to be taught in schools. The article highlights, first, how knowledge concerning sustainability in schools risks being reduced and made into knowledge about 'things'. Secondly, it also discusses how students in such a context risk being treated as instruments for ways of being in the world, rather than being subjects with ethical and political concerns for the world in which they live 'here and now'. Thirdly, as we explore through some empirical examples, such reduction and instrumentalism objectifies both students and nature, which makes an adequate response to the crises obsolete. As an alternative, the article develops a notion of grievability and its importance for adequately responding to all living beings within a project of sustainability. To this end, it develops suggestions for a transactive teaching approach in a time of climate crisis.