Abstract Relationships between 5- and 7-year-old children's communicative performance, and their level of understanding about message ambiguity and communication failure, were examined in three investigations. Communicative performance was assessed in terms of quality of instructions given for constructing a Lego model or a picture from felt pieces. The child speaker instructed the experimenter (Investigations 1 and 2) or another child (Investigation 3). Level of understanding about communication was assessed by asking the child to ascribe blame for communication failure following an ambiguous message, and to judge whether the speaker had told enough. In all three investigations, children with more advanced understanding about communication gave more detailed descriptions of pieces needed and supplied more information about positioning of pieces. In addition, in the first investigation those more advanced in understanding gave their instructions in a sequence more suitable for building. In the third investigation, child pairs more advanced in understanding communicated more effectively. It was suggested that the close association between communicative performance and understanding about communication occurred because the social experience which advances understanding, namely, the giving of explicit information when and/or why a listener fails to understand what the speaker means, at the same time encourages the child speaker to take responsibility for conveying a particular meaning unambiguously: the same experiences modify both communicative behavior and understanding about communication.