This article describes a case study of an expert teacher’s questioning strategies during an open-inquiry engineering curriculum in a Grade 4/5 classroom. The data sources collected over a 13-week period included videotaped whole-class and small-group teacher-student interactions, debriefing meetings after each lesson, interviews with observing elementary teachers, and stimulated recall sessions with both teachers present in the class. A holistic, sociolinguistic framework was used to analyze the transcribed videotapes. The analysis provides evidence for the complexity of questioning that is characterized by theinteractions of context and content of, and response and reactions to questions. The teacher’s competence in questioning was related to her discursive competence in the subject-matter domain, but question content was always mediated by the contingencies of discourse context and response and reaction patterns. The study also provides evidence that questioning is a complex practice which cannot be appropriated easily, a finding which implies a fundamental change in the professional preparation and development of science teachers.