This article describes a research project that aimed to classify different types of sustainability-related school tasks in terms of two central approaches in primary school education: action-based and task-based learning. Using a textbook analysis approach, the article clarifies implicit and explicit forms of sustainability education in school tasks in Luxembourgish science textbooks for Grades 1-6. The study uses a two-step analysis: first, scanning textbooks on content relating to sustainability; and, second, evaluating the teaching practices associated with this content apparent in the textbooks. Step one identifies the school tasks in which sustainability content is implicitly or explicitly addressed while step two analyzes which forms of action-based and task-based learning occur in these sustainability-related school tasks. Based on the results two claims can be made: first, that there is very little sustainability-related content in Luxembourgish primary science textbooks, and those topics raised mostly relate to sustainability only indirectly; secondly, action-based and task-based learning are undervalued in the context of sustainability-related school tasks; neither of the two was commonly found in school tasks in sustainability education.