Computer games can be considered complex learning environments in which players require instructional support to engage in cognitive processes such as selecting and actively organizing/integrating new information. We used meta-analytical techniques to test if instructional support enhances learning in game-based learning (k = 107, N[subscript adj] = 3675). We found that instructional support in game-based learning environments improved learning (d = 0.34, p less than 0.001). Additional moderator analyses revealed that the learning effect was largest when learning of skills was involved (d = 0.62, p less than 0.001) and when the instructional support aimed at the selection of relevant new information (d = 0.46, p less than 0.001). Furthermore, we found some evidence for a publication bias since the effect sizes for studies in peer-reviewed journals was significantly higher than for studies in proceedings and unpublished studies (journals: d = 0.44; proceedings:d = 0.08; unpublished: d = 0.14). (Contains 5 tables and 1 figure.)