Drawing on the Motivational Role Modeling Theory and Critical Mass Theory, the main objectives of this paper are to analyze the impact of Board Gender Diversity (BGD) on Employee Productivity (EP) and to investigate the moderating role of a Female CEO or a Female Board Chair on this relationship in Social Economy companies. The methodology used is a fixed-effects regression with panel data for 1,914 Spanish Social economy companies in the agri-food sector from 2017 to 2021. Our findings uncover a non-linear relationship between BGD and EP displaying a descendent curvilinear pattern, though not strictly U-shaped. Moreover, we confirm the moderating influence of a Female Chair, noting that its presence shifts the relationship between BGD and EP from an inverted curvilinear pattern to a U-shaped one. In this context, the board requires a minimum presence of women, set at a critical mass of 13 %. However, the moderating impact of a Female CEO remains inconclusive. This research underscores the significance of investigating board diversity, specifically emphasizing female leadership in understanding the link between BGD and EP. Moreover, to the best of our knowledge, this study is the first to explore the impact of BGD on EP by developing an integrated model based on Motivational Role Modeling Theory and Critical Mass Theory, and calculating the critical mass when a Female Chair is present on the board.