In this article, we draw on postfoundational frameworks to make visible the subjectification processes by which practitioners simultaneously master and become mastered by developmental theories. We emphasize the implication of the entire minded-body in the processes of the developmental worker formation. We show these processes through empirical investigation with data gathered through collective biography in a child development graduate course in a child and youth care program. Often developmental psychology masks itself as "just natural" knowledge that informs our practice. However, the article shows that our relationship with developmental psychology is much more intricate and intimate than we might believe. This intimate relationship can provide new possibilities for resisting developmental knowledge in practice and training.