This is a scanned copy of a thesis successfully submitted for the degree of Doctor of Philosophy in the Department of Psychology, University of Hull, U.K. in 1987. We learn language by using it. Interaction with others through language is essential for normal language development. Children with delayed or impaired language may therefore benefit from additional experience of interacting through language in structured situations. This thesis explores how computers might help provide this experience. It reports a project in which programs were developed to hold written dialogues about screen objects, and observed in use by deaf and other language-impaired children. This version is published through www.lulu.com who should be able to supply it at the best price, and from where it can also be downloaded more cheaply in electronic form.