In this study, a collaborative game-based learning environment is developed by integrating a grid-based Mindtool to facilitate the students to share and organize what they have learned during the game-playing process. To evaluate the effectiveness of the proposed approach, an experiment has been conducted in an elementary school natural science course to examine the students' performance in terms of their learning attitudes, learning motivation, self-efficacy and learning achievements. From the experimental results, it is found that the Mindtool-integrated collaborative educational game not only benefits the students in promoting their learning attitudes and learning motivation, but also improves their learning achievement and self-efficacy owing to the provision of the knowledge organizing and sharing facility embedded in the collaborative gaming environment. (Contains 3 figures and 5 tables.)