Agri-environmental schemes (AESs) have been implemented in many countries in Europe. However, there is mixed evidence about their effectiveness. Several studies in different countries suggest that AESs are more effective when designed at landscape level and implemented by groups of collaborating farmers ('farmer collectives'). The EU Common Agricultural Policy (CAP) has enabled groups of farmers to be applicants for and final beneficiaries of AESs subsidies for the period 2015-2020, but it is unclear what is needed for farmer collectives engaged in AESs to contribute to more agrobiodiversity. In this paper, the lens of 'professionalization' is used to conceptualize and operationalize the performance of farmer collectives. We have developed an assessment framework that facilitates the characterization and development of the degree of professionalization of farmer collectives. The ultimate aim is achieving ecological effectiveness of AESs by professionalization of the farmer collectives. The framework distinguishes three categories of professionalization: organizational, occupational and systemic, and provides a new lens for research on AESs. It can also be used by practitioners involved in AESs to provide insight into, and reflect upon, the performance of farmer collectives.