http://journals.sagepub.com/doi/abs/10.1177/1046878105282276

Many people believe that educational games are effective because they motivate children to actively engage in a learning activity as part of playing the game. However, seminal work by Malone, exploring the motivational aspects of digital games, concluded that the educational effectiveness of a digital game depends on the way in which learning content is integrated into the fantasy context of the game. In particular, he claimed that content that is intrinsically related to the fantasy will produce better learning than that which is merely extrinsically related.