A dynamic systems (DS) approach was used to study changes in the structure of family interactions during the early adolescent transition period. We hypothesized that the age of 13-14 years, for boys, constitutes a developmental transition period marked by a peak in the variability of family interactions; before and after this period, interactions were expected to be stable. Longitudinal observational data were collected in five waves prior to, during, and after the transition period. Boys (n = 149 families) were videotaped problem-solving with their parents at 9-10 years old, and every two years thereafter until they were 17-18 years old. Based on these observational data, state space grids (a new DS method) were constructed for all families across all waves. Two variables indexing the variability of the family interactions were derived from the grids. As hypothesized, statistical analysis of these DS variables revealed a significant quadratic effect related to a peak in variability at 13-14 years of age.