Characterizing a new dimension of change in attending and responding to the substance of student thinking

"Responsive teaching," in which teachers attend and respond to the substance of students' ideas, is central to facilitating student learning through engagement in authentic disciplinary practices. In characterizing teachers' progress toward greater responsiveness, researchers typically code teachers' attention as shifting toward the intellectual content (substance) of students' ideas and away from other foci such as students' correctness. These schemes, however, do not distinguish between different aspects of the substance of students' ideas. In this paper, we argue that a science teacher, Mr. S, demonstrates progress not by shifting toward greater attention to "substance," but rather by shifting in the facet of student thinking to which he primarily attends and responds. He shifts toward attending to causal stories (mechanistic explanations) and away from causal factors (potentially relevant variables). We argue that such shifts toward more sophisticated epistemic practices should be targets of professional development and of the assessment of responsive teaching.