A longitudinal study, intended to produce a profile of the relationship between cognitive, social, and linguistic development in Danish children, had as subjects a boy and a girl aged 11 and 8 months, who were observed until they reached age 3. Naturalistic language used by the children and their parents, videotaped during regular visits, was analyzed for utterance length and vocabulary and for changes in these factors over time. Significant individual differences could not be explained by simple applications of cognitive theory. Application of a theoretical framework that distinguishes between analytic and holistic processing strategies to explain similarities and differences between the children puts into question the surface validity of some of the objective measures used in language development research. It is suggested that individual differences in development demand a more refined approach than the generalist approaches used in recent years. (MSE)