This chapter revisits Clancey's application of transactional perspectives to Lehrer and Schauble's classroom episodes ("A Transactional Perspective on the Practice-Based Science of Teaching and Learning"). Interpreting these episodes with a focus on the specific and contingent role of disciplinary or content knowledge, children's engagement, and the potential to improve teaching, Confrey identifies three key issues: (1) the role of competing conceptions, (2) typicality and bin size, and (3) variability, predictability, and spread. She then examines the applicability of Clancey's theory to identifying such critical elements, and its potential to contribute to a practice-based science of teaching and learning.