To identify aspects of family behavior associated with glycemic control in youth with type 1 diabetes mellitus during the transition to adolescence, the authors studied 121 9- to 14-year-olds (M = 12.1 yrs) and their parents, who completed the Diabetes Family Conflict Scale (DFCS) and the Diabetes Family Responsibility Questionnaire (DFRQ). From the DFRQ, the authors derived 2 dyadic variables, frequency of agreement (exact parent and child concurrence about who was responsible for a task) and frequency of discordance (opposite parent and child reports about responsibility). The authors divided the cohort into Younger (n = 57, M = 10.6 yrs) and Older (n = 64, M = 13.5 yrs) groups. Family conflict was significantly related to glycemic control in the entire cohort and in both the Younger and Older groups. However, only in the Younger group was Agreement related to glycemic control, with higher Agreement associated with better glycemic control. Findings suggest that Agreement about sharing of diabetes responsibilities may be an important target for family-based interventions aiming to optimize glycemic control in preteen youth.