kindergarten through middle school, will need help to recognize the distinction between disagreeing with an idea and disagreeing with a person.

Mediating effective scientific argument also requires the teacher to have sufficient knowledge to perceive—on the fly—what is scientifically productive in students’ talk and what is not. Younger students, English language learners, or students exploring a new topic will tend to use language that is ambiguous, fragmentary, or even contradictory—especially in a heated conversation. In these moments, the content and structure of students’ arguments can be difficult to follow. Yet if the educational goal is to help students understand not only scientific outcomes and the concepts that support them but also how one knows and why one believes, then students need to talk about evidence, models, and theories.

Position-Driven Discussion

In Chapter 4, we saw a class engage in a collective discussion about whether adding air to a volleyball would increase its measured weight. This discussion and the ensuing activity involved all of the students in a teacher-guided, whole-group discussion. This was a discussion of a very specific kind—what might be called a “position-driven” discussion. It involved a demonstration that was poised to run but was not run until after students exchanged predictions, arguments, and evidence. The proposed problem had more than one imaginable outcome, so the students could predict and argue for different outcomes. In addition, it featured materials and scenarios familiar to the students, so that each student believed that they could anticipate the outcome. By using familiar materials and phenomena, students can more readily conjure up their own ideas and experiences and tap into these as they build explanations. This makes it possible for every student to participate in a more meaningful way.

A position-driven discussion generally forces the student to choose from two or three different but reasonable answers. In the case of the students in Mr. Figueroa’s class in Chapter 4, the students had to decide whether the volleyball with 15 extra pumps of air would be (1) heavier, (2) lighter, or (3) weigh the same. This kind of discussion generates productive and lively talk. It also calls on students to actively participate in reasoning, theorizing, and predicting. Students take positions and attempt to formulate the best arguments and evidence they can in support of their position. Sometimes, informal votes are taken to see where the students stand with respect to one another, followed by more opportunities

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