## Pedagogy

Each LC lesson consists of three sections. First a brief Purpose and Key Question(s) section gives the rationale for the lesson and provides the lesson' focus. (This section may include Materials Needed for lessons where students do experiments with simple materials. The use of hands-on materials is optional, as there are videos available showing each of the experiments being performed.) The second and major portion is the Predictions, Observations and Making Sense (POM) section. The questions in this section guide students through predictions, observations and inferences to help them answer the key question(s). The choice of questions was informed by the extensive literature on students' understanding of physical science. The POM section often begins with a clicker question about a scenario to elicit students' prior knowledge. Instructors can collect student responses and project the results for the class to see. Occasionally, instructors may wish to ask students to share their reasoning for particular choices — without judging which answer is the 'best.' Videos of demonstrations, experiments, or simulations (or optional hands-on experiments, if they can be performed on a chair desk), typically follow and provide evidence for students to consider. Students record their observations on the lesson sheets and answer questions to guide their interpretations of the evidence. The POM section continues with additional clicker questions (typically following discussion with neighbors), videos and making sense questions. Occasional narrative text and/or diagrams introduce new terms or new ways of describing the situation (e.g., diagrammatic representations). The final Summarizing Questions section consists of one or two clicker questions designed to see if students have synthesized the main ideas from the lesson. At this point, students are expected to come to consensus on the appropriate scientific idea(s). Most LC lessons are intended to take 25-75 minutes of class time.

As an example of the LC lesson structure—and the way the Next Gen PET Design Principles are incorporated—consider Lesson 1 from the Force Model Unit of the Interactions and Forces Module. Lesson 1 introduces students to the force description of interactions. One of the key questions is: When does the force of a quick push stop acting on an object? The pedagogical purpose is to immediately begin addressing the common idea that 'force' is something that an object carries along with it and is transferred between objects when they contact each other [1-5]. Compared to physicists, students often ascribe a different meaning to the word 'force,' and often talk about the 'force of an object,' as if it were a property of the object. This lesson provides students with evidence that a force is an interaction between two objects, not something carried by an object or something associated with an individual object.

The Predictions, Observations and Making Sense (POM) section includes three parts; Part 1 addresses the Key Question on brief pushes. Students first watch a movie of a person giving a low-friction cart a quick push to get it moving along a track. They then consider the clicker question shown in Figure 1. This question follows from Design Principle 1 (Learning builds on prior knowledge). The choices are based on students' common responses to similar, but open-ended questions in the SC version of Next Gen PET and predecessor curricula, which suggested reasoning such as: the force is applied for only a very short time, after which the cart speeds up before starting to move with constant speed (choice A); the cart must speed up 'just a little' after the contact is finished (choice B); the force stops as soon as contact is lost (choice C); as long as the cart is in motion (even after contact is lost) it is influenced by the force of the hand, or the force is carried along as the cart moves (choice D). While the clickers provide quantitative information on students' responses, the instructor must interpret the results based on previous experience or knowledge of the literature on students' ideas on force and motion. The instructor resources provide relevant information and sample clicker response patterns.

Next, the materials include a movie of a low-friction cart being given three quick pushes as it moved along a track, with the speed-time graph displayed. In the corresponding SC activity, students generate the speed-time graph themselves. In the LC format, it is not feasible for students to conduct the experiment themselves, but including the movie supports the norm that arguments in science should be based on evidence (Design Principle 5: Learning is facilitated through establishment of norms). The next clicker question asks the students to imagine what force-time graph would correspond to this speed-time graph, and choose from three possible graphs (see Fig. 2.). Again, the distractors are drawn from the developers' experience with the SC version and other curricula, and represent typical student responses. These include the idea that the force is transferred to the cart during each push, but that the force slowly runs out after the push (choice C); and the idea that whenever there is motion, there must be force, and that more speed means more force (choice B).

The materials next include a movie with the cart being given three successive pushes, with both speed-time and force-time graphs being generated from motion and force sensors. The class should agree that the evidence supports graph A from CQ 1-2. Next students watch a simulation of object receiving brief pushes. Part 1 of the POM section ends with several making sense questions to help students interpret and draw conclusions from the movie and simulation. The last making sense question focuses on the issue of transfer: According to the evidence from the graphs, did the force caused by the hand continue acting on the cart after it had lost contact with the cart? How do you know? After students discuss the questions with their nearest neighbors, the instructor can call on students in the class to share their answers and reasoning with the whole class.

Part 2 of the POM section addresses the question of whether an object being in motion implies that a force is acting on it. Part 3 connects force and energy in terms of what is transferred during a contact interaction. The Summarizing Questions section begins with a clicker question specifically about transfer, shown in Figure 3.

Lesson 1 illustrates how Next Gen PET incorporates the Design Principles. Students' prior knowledge is elicited through the first clicker question (supporting Design Principle 1), providing opportunities for students to engage in discussions (supporting Design Principle 4). Videos, clickers, and the student workbook are tools that facilitate learning and help structure interactions (Design Principle 3). Next Gen PET also promotes norms (Design Principle 5) that ideas should be supported by experimental evidence, that scientific ideas should make sense, that students need to take an active role in learning, and that students are expected to contribute ideas to group and class discussions. On a larger scale, Lesson 1 is part of a unit that successively builds the complex ideas associated with force and motion (Design Principle 2).

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This project is funded by the National Science Foundation IUSE program, DUE-1626496. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.