The implementation of large-scale intervention and development projects is often problematic, and the impacts of such projects usually fall somewhat short of what was expected. Additionally, the rationalities of intervention projects are not carried over into classroom teaching as directly as expected. This problem is generally known, but comprehensive explanations continue to elude the research community at large. Using the theory of cultural-historical activity theory (CHAT), we propose that the heart of the problem lies in the expansive learning process that teachers undergo. This process is driven by unrecognised contradictions in terms of cultural and historical origin, which are fundamentally different from the processes governing the projects. We analyze two cases taken from two large Danish professional development projects. In each case, we focus on a teacher as part of two activity systems (‘the project’ and ‘the classroom’) and how the contradictions within and between these shape learning through epistemic actions. The results indicate the importance of making these contradictions apparent and accessible to everyone in the activity systems. Because of these various contradictions, the agency conferred upon teachers leads to unintended outcomes.