What constitutes a successful lesson? A considerable body of literature examines instructional talk; however, little attention has been directed to situations in which teacher intentions (as captured by lesson plan) are stymied by unanticipated student response and the teacher must instantaneously reevaluate and revise an intended lesson. This article scrutinizes specific teacher discourse practices in one English language learner (ELL) classroom when students struggle with a text. Close discourse analysis reveals that this teacher's consistent guided practice of anchoring her questions in student contributions to support students' existing purposes and understandings is not compromised even when this results in extended vocabulary-centered student searches for meaning and a lesson very different from what she intended. The dialogic nature of this lesson talk challenges simplified dichotomies of closed and open questions, as well as established notions of efficient and effective instructional practice. This illustrative case of dialogic teaching explicates the role of contingency in interactive discussion.