Scaffolding for Challenge-Based Learning in Sustainability Education: A Multiple-Case Study

Challenge-based learning (CBL) is a student-centered approach engaging learners in complex, open-ended problems. While such openness can foster deeper learning and creativity, it also demands high self-direction. Teachers must therefore provide sufficient scaffolding without undermining CBL’s authenticity. This study examines how secondary education teachers design and enact scaffolding in sustainability-oriented CBL projects, and how students experience this support. A multiple-case study of three projects distinguished soft scaffolding (adaptive, just-in-time support) from hard scaffolding (predefined tools and structures). Data included teacher interviews ( n = 3), student focus groups ( n = 18), and classroom observations. Findings showed the scaffolding type and function depended on project open-endedness, teacher readiness, and alignment with project focus. In the most open-ended project, the teacher mainly used soft scaffolding to guide thinking and decision-making, whereas more structured projects relied on hard scaffolds for procedural support. Students’ experiences varied: some thrived under autonomy, developing ownership and engagement, while others needed more explicit guidance. These results suggest that scaffolds should align with project goals, be explicit in their contribution to progress, match students’ readiness for self-directed learning, be enacted by teachers comfortable in a coaching role, and include affective support to help students manage frustration and uncertainty.