A study of child language development that takes a combined developmental and functional view of language acquisition is reported. It has three parts. The first outlines a variety of functional approaches in linguistics, links linguistic theory with what is known about children's emerging conceptual and social development, particularly in the areas of agentivity and control, and describes the methodology of the study reported. The second part presents an analysis of six children's language development, three of whom are ego-anchored and three of whom are not. These case studies focus on the protracted nature of language development as viewed from the functionalist perspective. The third part elaborates on mechanisms of development, presenting various proposals concerning the organizational and re-organizational processes, drawing on both conceptual and environmental accounts. Further areas of research are suggested. A substantial bibliography and author and subject indexes are also included. (MSE)