This paper studies students' unexplained answers and how teachers respond. The data is from observations of teaching in five different classrooms at Norwegian upper primary schools. Using frameworks and concepts usable to describe classroom discourse on a turn-by-turn basis, it is found that teachers more often attend to details of how and why when responding to unexplained answers than in general. This creates opportunities to learn for the students and opportunities for teachers to gather information usable for formative assessment. It is also observed that these teachers rarely attend to details of how and why when students answers incorrectly and by this limiting opportunities to learn.