Early years mathematics classrooms can be colourful, exciting, and challenging places of learning. Andrea McDonough and fellow teachers have noticed that some students make good decisions about using materials to assist their problem solving, but this is not always the case. These experiences lead her to ask the following questions: (1) Are concrete materials necessarily helpful for all students in their learning of mathematics? and (2) Are concrete materials always used as effectively as they might be? The focus of this article is the use of concrete materials in the early years mathematics classroom, but the issues and questions might apply equally to virtual manipulatives and to use of manipulatives in higher year levels. With the underlying belief that "good concrete activity is good mental activity" (Clements & McMillen, 1996, p. 272), three key messages are discussed. These are that: (1) concrete materials can help students focus on key mathematical ideas; (2) lessons that incorporate concrete materials can stimulate children's higher order thinking; and (3) teachers may need to intervene when students use concrete materials.