This paper describes a child’s mental model of an Embodied Conversational Agent (ECA) acting as a learning Companion. Embodied Conversational Agents are characters that interact with humans through the medium of conversation. Acting as a learning Companion, an ECA can support children or offer guidance toward improving the learning process. When a child uses an ECA they necessarily form some sort of mental model of the ECA and this will affect the manner in which they learn and ultimately determine the effectiveness of their learning. This paper considers what a child’s natural mental model of an ECA is, and how we can best develop an ECA interaction strategy to fit that mental model.