Forty-five mothers and grade 6 girls were observed during three discussions at each of four longitudinal waves spaced 6 months apart. All girls entered a new school in grade 7 (Wave 2) and flexibility was expected to peak at this transition. Within each wave, discussions progressed in an A-B-A sequence of emotional valence: positive, conflictual, and positive. Measures of Negative Emotion and Flexibility were derived from a novel dynamic systems method, state space grids, created from the coded observations of these discussions.The entrance into adolescence is marked by changes in multiple domains that have an impact on adolescent emotions and emotion regulation, especially within the context of family interactions. Changes in mother-daughter emotion-related flexibility tapping individual differences in emotion regulation across the early adolescent transition were examined through a dynamic systems approach. There were two objectives: (1) to replicate and extend a study that found that the flexibility of parent-boy interactions peaked in early adolescence in a manner consistent with a developmental phase transition (a period of instability and high variability observed when one stable pattern or structure breaks down and a new structure emerges in its place); (2) to resolve the conundrum that emerged from the consideration of three sets of research findings: (a) negative emotion reduces flexibility, (b) negative emotion increases during early adolescence, yet (c) socioemotional flexibility peaks in early adolescence. I hypothesized that negative emotions reduce flexibility by eliciting emotion regulation strategies that constrain behavior but that these regulatory strategies go through a period of instability during the upheaval of early adolescence.As expected, Negative Emotion was higher and Flexibility was lower in the conflict discussion than in either positive discussion. Negative Emotion increased linearly over the four waves. However, those without added stress at the school transition peaked in flexibility, as hypothesized. In contrast, stress at the transition appeared to reduce flexibility in grade 7. The implications of these real-time and developmental profiles are discussed.