Despite the increasing attention of management scholars to boards of directors, there is still scant evidence on the antecedents of board task performance. The lack of significant results seems to be due to some theoretical and methodological choices followed by scholars, i.e. the almost exclusive reliance on agency theory and the use of demographic data. Following the call for dismantling the fortresses dominating past studies, this paper contributes to opening the ‘black box’ of boards of directors, developing a conceptual model that considers the impact of board members' diversity, commitment and critical debate on board task effectiveness in performing its service and control tasks. We collected primary data through a questionnaire survey, and we tested the model controlling for board, firm and industry characteristics. Our findings suggest that (i) the predictors we identified, and particularly the board members' commitment, are far more important than board demographics to predict board task performance; (ii) firm and industry contexts exert a significant influence on board task performance; (iii) predictors have a different impact on specific sets of tasks. Thus, our findings support the idea that several board characteristics and contingencies at both industry and firm level must be acknowledged in board design.