This paper summarizes and illustrates an approach to assessment of communication development and treatment which focuses on the early relationships of preconversational children with their significant adults. The assessment approach is part of the Ecological Communication (ECO) model, which views caregivers of delayed children as critical to the communicative development of children, as their use of interactive and communicative strategies allows the children to learn spontaneously from them during frequent, habitual conversational exchanges. The model focuses on five developmental competencies: becoming play partners, becoming turn-taking partners, becoming nonverbal communication partners, becoming language partners, and becoming conversation partners. The paper presents a brief history and theoretical framework for the approach; reviews the dimensions of the ECO model with an emphasis on assessment; and illustrates the approach with case studies, one for each of the five developmental competencies. Appendices contain assessment instruments and handouts. (48 references.) (JDD)