According to theory, maternal sensitivity should be associated with attachment security in middle childhood. We measure two aspects of maternal sensitivity—affective understanding, a component of parental mentalization, and affective synchrony, a component of parental empathy. We tested our hypotheses within a diverse sample of school-aged children (48.6% female, M _age = 10.27, SD _age = 1.09) and their mothers (N = 112 dyads) at baseline and after a standardized laboratory-based stressor in which children worked on unsolvable puzzles while their mothers watched. Results revealed no significant associations at baseline, but lower maternal attachment avoidance and greater child attachment security were associated with greater affective understanding and greater affective synchrony after the stressor task.