A reciprocal model of language development is proposed analogous to Bowlby's model for the development of attachment, a control system model. The hypothesis for the research reported is that a reciprocal behavioral system operates between the language-developing infant-child and the competent language user in a socializing-teaching-nurturing role vis-a-vis the language-developing child. Findings are from a longitudinal study of four infant-mother dyads, videotaped in the home from the time the infants were 3 months until they were 2 years old. The mother's linguistic behavior following vocalizing and verbalizing by her infant is analyzed for evidence that it is language-teaching behavior appropriate to the infant's level of linguistic development and, in the terms of the control system model, elicited by the infant's linguistic behavior.