Background: An increasing amount of empirical attention is focused on adrenocortical synchrony as an index of biobehavioral co-regulation between parent and child in the context of early child development. Working with an ethnically diverse community sample of children (N = 99, 50.5% male, ages 9-12), we collected saliva samples from mother-child dyads prior to and after a laboratory-based performance challenge task, and tested whether maternal overcontrol and child age moderated dyadic synchrony in cortisol. Results revealed that cortisol levels between mothers and children were significantly positively correlated at pretask for dyads with mean age and older children only, at 25-min post-task for all dyads, and at 45-min post-task for all dyads. Higher overcontrol/older child dyads exhibited a unique pattern of cortisol synchrony wherein at pretask, mother-child levels had the strongest positive correlation, whereas at 25 and 45 min, mother-child cortisol levels were significantly inversely correlated. These findings contribute to theory and research on parent-child relationships by examining parenting behavior, developmental stage, and adrenocortical synchrony in tandem.