This study presents a model of non-structural factors that affect the effectiveness of boards of directors in monitoring strategy implementation - SI. Despite the intense debate on the contribution of corporate governance to the strategic success of firms, no studies have analyzed systematically the antecedents of the SI monitoring task that boards are expected to perform. Building on general board performance models, this study used a Team Production Theory perspective (Blair and Stout, 1999) to identify the factors that may influence a board’s performance in ensuring SI. A two-step research method was used. The first step consisted of in-depth interviews with a panel of experienced board directors. The interviews generated insight to delimitate a preliminary analytical framework that was built from literature. This framework is, in itself, a research product that may be used to ground future studies. The second step was a survey with 217 board directors of Brazilian companies. The collected data were analyzed by the method of structural equations - SEM, in order to cope with simultaneous relationships among constructs and measurement errors. Four competing and theoreticallygrounded structural models were analyzed for fit and explanatory power. The final model included five explanatory constructs of Board Effectiveness in SI Monitoring: Board Chairperson Leadership, Access to Information, Business Knowledge, Board Work Dynamics and Attention to SI Monitoring. The model confirmed all the hypothesized relationships among the constructs and explained 54 per cent of the variance observed in Board Effectiveness in SI Monitoring. The results revealed multiple mediations among the constructs. Board Chairperson Leadership was positively associated with Access to Information, Board Work Dynamics and Attention to SI Monitoring. This suggests that a board chairperson with superior leadership attributes may simultaneously influence several factors that impact the board’s strategic monitoring performance. In addition, the results showed that boards that have more access to information may display a work dynamics that is conducive to performance in monitoring SI. As expected, a board’s effectiveness in the SI monitoring task was found to depend directly on the level of attention devoted to it. This suggests that the adoption of internal policies and norms that include the SI monitoring task in the board’s agenda will improve its performance in the task. The actual functioning of boards is a hitherto under-researched phenomenon due to widely acknowledged empirical difficulties. By investigating the nature of the relationships among the antecedents that affect the quality of a board’s intervention into the SI process, and by analyzing them in a non anglo-american empirical setting, this study aims to make an innovative contribution to the knowledge and management practices in the fields of corporate governance and strategic management.