Teachers' agency is required to cope with the challenge of designing Technology Enhanced Learning (TEL) activities. Relying on third generation Activity Theory, this study addresses the theoretical underpinnings that led to a formative intervention inspired by the Change Laboratory methodology to support in-service French Literature teachers in a secondary school engaged in transforming teaching-learning activity by designing TEL scenarios. This study introduces a card deck as a mediating artefact to support teachers' co-design of Technology Enhanced Learning (TEL) scenarios.