Role Attribution         In a PBL class, a problem is given to a small group of students. Although medical schools have been known to use groups of around 10 students, groups of three or four students are ideal at the college level. Using the model established at the University of Minnesota for small groups (http://groups.physics.umn.edu/physed/Research/CGPS/GreenBook.html), we can assign a specific role to each student. Since the resolution of the problem requires planning and monitoring strategies, students are given roles that integrate these tasks.       •The manager proposes plans of action and makes sure that the group discussion is progressing smoothly and that all members participate. •The skeptic questions ideas put forward as constructively as possible. •The checker/recorder writes down and organizes the different ideas proposed and makes sure that all group members are able to explain the solution. •The energizer/summarizer reinvigorates the discussions when they taper down and monitors the decisions put forward and their rationales.       What does the teacher do?         During a PBL class, the teacher acts as a guide on the side, rather than a sage on the stage. It is important for the instructor to guide students’ inquiry without directly instructing students on possible action paths that would provide solutions to the problem. Thus, instructors may guide a discussion if it moves off track, but should not give answers to students.         Approaching the Problem: the Three-Step Cycle         Since PBL problems are intentionally ill-structured (students are not told what steps to carry through to solve the problem), the solution should not be immediately foreseeable. To solve the problem, students should be guided to use the three-step cycle consisting of: what we know, what we need to know and summary.         1. The first step a PBL group should adopt is to sift out what is important from what is superfluous in the problem and establish a list of facts. This first phase of the cycle is referred to as the “what we know” step, although only the selected important information known should be recorded.         2. Once students have established a list of facts, some information required to solve the problem will be missing. Therefore, students should use their list of facts to generate a second list of “what we need to know.” Elements of this second list may be generated from a combination of elements of the first list (for instance, students may know the net force on an object and its acceleration, and use this to infer its mass, which in turn may be one of the missing elements required to solve the problem). This step thus requires students to collectively define the formal problem to be solved and determine what intermediate steps can be solved in order to achieve a global solution.         3. The last step allows students to monitor their progress and reshape their objectives from their current state of knowledge. Indeed, in the first step, relevant information is gathered. As a formal question is asked in the second step, some of the initially relevant information may have lost its importance. Therefore, one needs to return and summarize the current state of “what we know.” The same review-summarizing process applies to the second step of the cycle. Indeed, some hypotheses of “what we need to know” may have been rejected and can therefore better orient “what we need to know” as well as “what we know.” Therefore, this last “summary” step is the one that calls on the students to monitor their thinking by returning to the initial two steps of the cycle and re-evaluating “what they know” and “what they need to know.” As new facts are generated, it is useful to make a summary (step 3, final step of the cycle) to manage the information flow.         For example, a car crash problem is given to students for them to learn about motion (1-D kinematics). The global problem is to find the whether the driver was driving recklessly.         1. To achieve this goal, students will need to collect information about the context (what we know: definition of recklessness: driving under the influence, driving 30 km/h above the speed limit).         2. To determine whether the driver was reckless, more information is required, such as whether the driver was intoxicated or whether the driver was speeding (what we need to now: driver’s blood alcohol level, driver’s initial velocity).         3. As new bits of the puzzle are generated (e.g., a negative tox screen), a summary forces students to re-evaluate what they know and what they need to know. (They now know that the driver was not intoxicated; therefore, they need to know whether the driver was speeding. In turn, they must determine from the problem how to gather relevant data indicative of the driver’s speed on impact.)         Note that, for students, the problem itself is meaningful (a car crash, just like on TV!), but ill-defined (what must I do to find out?). It is now up to the student to define the actual problem to solve (find the speed of the car on impact).         Problem Solution         To solve the problem, PBL students have to define a structured, step-by-step approach to the solution. In traditional instruction, students are handed a cookbook list of steps to solve a given problem (Part A: solve for velocity; Part B: solve for Δx; and so on). In this case, students may struggle with performing some of the steps, or with the implicit meaning of these steps, or worse yet, fail to recognize how each of these steps leads to a global solution to the problem. In a PBL approach, however, students must generate their own step-by-step method to solve each problem. Thus, although difficulties will arise in carrying out a given step, no confusion exists on the sequence or meaning of each step required. Furthermore, as students work to solve the problem, various solution paths emerge between groups. Students therefore view problem solving as a creative process that can take many forms within a given set of constraints. To paraphrase the late Nobel laureate Richard Feynman: Good scientists always know at least three ways to solve the same problem. Contrary to traditional problem solving activities where one preferred solution is usually presented, many solutions are possible to any given problem. PBL activities enable students to appreciate that problem solving is not a uniform one-size-fits-all kind of activity and that many solution paths are possible.