Abstract This article discusses a number of common interpretations of ‘implementation’ in the literature, and how these have been confused. Various different levels of implementation are then discussed, including the concept of model effectiveness. This is concerned with both the operational effectiveness of the model, as shown by a tangible improvement in the system modelled, and the personal effectiveness in helping users learn more about the system itself. Research is then described to explore various aspects of model usage and effectiveness. The research took place in the context of a business game used by a large number of practising managers. An unusual feature of the game was the fact that participants were offered the use of a number of models to aid their decisions. The usage of the models, and their effects, were measured objectively. Results showed that models were used extensively, and their effects were advantageous in a number of ways. The implications of this work are discussed.