The conservation sector increasingly values reflexivity, in which professionals critically reflect on the social, institutional and political aspects of their work. Reflexivity offers diverse benefits, from enhancing individual performance to driving institutional transformation. However, integrating reflexivity into conservation practice remains challenging and is often confined to informal reflections with limited impact. To overcome this challenge, we introduce co-reflexivity, offering an alternative to the binary distinction between social science on or for conservation, which respectively produce critical outsider accounts of conservation or provide social science instruments for achieving conservation objectives. Instead, co-reflexivity is a form of social science with conservation, in which conservation professionals and social scientists jointly develop critical yet constructive perspectives on and approaches to conservation. We demonstrate the value of co-reflexivity by presenting a set of reflections on the project model, the dominant framework for conservation funding, which organizes conservation activity into distinct, target-oriented and temporally bounded units that can be funded, implemented and evaluated separately. Co-reflexivity helps reveal the diverse challenges that the project model creates for conservation practice, including for the adoption of reflexivity itself. Putting insights from social science research in dialogue with reflections from conservation professionals, we co-produce a critique of project-based conservation with both theoretical and practical implications. These cross-disciplinary conversations provide a case study of how co-reflexivity can enhance the conservation–social science relationship.