Abstract. Betty’s Brain is a teachable agent system in the domain of river ecosystems that combines learning by teaching and self-regulation strategies to promote deep learning and understanding. Scaffolds in the form of hypertext resources, a Mentor agent, and a set of quiz questions help novice students learn and self-assess their own knowledge. The computational architecture is implemented as a multi-agent system to allow flexible and incremental design, and to provide a more realistic social context for interactions between students and the teachable agent. An extensive study that compared three versions of this system: a tutor only version, learning by teaching, and learning by teaching with self-regulation strategies demonstrates the effectiveness of learning by teaching environments, and the impact of self-regulation strategies in improving preparation for learning among novice learners.