Mobile text messaging provides a novel opportunity to engage learners in collaborative learning experiences. This study describes the use of mobile text messaging to engage learners in an interactive role-playing game based on the water cycle. Learners were guided through their role in this participatory simulation using SMS messages sent to their mobile phones. Learners physical positions in the game triggered particular events and precluded others, thus enabling an interactive simulation that was more than just a series of messages sent out at fixed intervals. Results indicated that the learners understanding of the topic was at least as good as in a comparative conventional teaching condition, despite being given far less causal information. Furthermore, a set of learners who answered a test of water cycle knowledge without any teaching gave different responses to the SMS group, suggesting that the SMS game is at least a viable and entertaining alternative to lesson-based teaching for appropriate topics.