Introduction The flipped classroom environment has become increasingly popular in recent years. In a flipped classroom, students watch video-recorded lectures at home which frees time to engage them in socially-mediated, active learning in class. 1 The flipped class instructional design is based on the principles that class time should be used to elicit deep thinking and that students learn better through discussion and negotiation with their peers. Thus, appropriate activities focus on the

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... difficult aspects of learning a subject. While there has been attention to the mechanics and principles of how to deliver the lecture component asynchronously, 2,3 or the effectiveness of a flipped classroom relative to traditional instruction, 4-6 less attention has been given to systematically explore the most effective instructional strategies for the in-class activities within the flipped classroom. In this paper, we look at in-class activities in a flipped classroom directed at cultivating deep conceptual understanding. Engineering educators and industry partners emphasize the need for students to apply their knowledge to new and challenging problems. 7 In order to do so, students must learn with understanding. 8 A lack of conceptual understanding has been shown to severely restrict students' ability to solve new problems, since they do not have the foundational understanding to use their knowledge in new situations. 9 However, traditional lecture-based instruction often reward students more for rote learning and algorithmic substitution than for conceptual understanding. 10 As a result, many of our classes are ineffective for developing students' understanding of fundamental concepts. 11 This study investigates active learning activities in a flipped classroom aimed at a common misconception in heat transfer -the Rate vs. Amount misconception in which students conflate the rate of energy transferred and the amount of energy transferred. We compare two inquirybased in-class activities developed with different strategies, one based on a cognitive conflict strategy and the second an analogy strategy. The research question we ask is, "How do the measured learning gains of the Rate vs. Amount concept compare when students complete an inquiry-based activity developed with a cognitive conflict strategy to one developed with an analogy strategy?" Theoretical Framework Synthesizing the flurry of research and instructional development activity on conceptual change in the 1980s, Scott, Asoko, and Driver 12 cite three levels of pedagogical decisions that are needed in designing instruction to foster conceptual change: learning environment, teaching strategies, and learning tasks. The learning environment is at the highest level and provides the affordances for activities and support needed for learning. At the second level, the teaching strategy guides the overall design and sequence of instructional activities. Finally, the learning tasks sit at the finest level; they comprise the specific activities students are asked to complete to promote conceptual change. Our study design focuses on the second level of teaching strategies for conceptual change. Scott, Asoko and Driver 12 divide effective reform strategies into two broad groupings. The first Page 26.375.2 grouping refers to strategies that seek to elicit cognitive conflict and create "teachable moments" through the resolution of the conflicting perspectives. The second grouping contains strategies that seek to build on and extend existing ideas, often using metaphor or analogy. Cognitive conflict strategy The first activity is based on a cognitive conflict strategy for conceptual change. Strategies based on cognitive conflict, also referred to as cognitive dissonance, 13 stem from a constructivist perspective of learning in which the learner's active part in reorganizing their knowledge is critical. 8, 14 Posner and colleagues 15 propose that four stages are needed for conceptual change. The stages include: (i) dissatisfaction with current conceptions, followed by a new conception that is (ii) intelligible, (iii) plausible, and (iv) potentially fruitful. The goal of the cognitive conflict inquiry-based method is to produce a teachable moment for students by promoting cognitive conflict and leading the learner through these four stages. To initiate this process, the instructor puts students in situations where they make a commitment to and then unavoidably confront a misconception to promote dissatisfaction. This strategy was used by the Activity-Based Physics group to develop inquiry-based activities in Mechanics and has extensive empirical support for its effectiveness. [16] [17] [18] Building on this success, engineering educators have adopted this strategy for instruction in heat transfer, 19 thermodynamics, 19 and dynamics. 20 However, questions have arisen about the effectiveness of the cognitive conflict strategy for promoting conceptual change for several reasons. 21 First, students simply sometimes ignore the conflicting information. Second, while higher performing students might embrace the "conflict," less successful students have been observed to try to avoid the conflict and thereby develop negative attitudes. Third, there may not be support to reconstruct a normative conceptual understanding following dissatisfaction with the original misconception. Finally, as Smith, de Seessa and Roschelle 22 argue, this strategy potentially undermines student confidence in their sense-making abilities. Analogy strategy The second activity is based on an analogy strategy, which also has long been advocated as a strategy for promoting conceptual change in science. 23 An analogy connects a new concept or topic, the target domain, to situations or experiences which are more familiar, the source analogy. This strategy focuses more on providing scaffolding for students to learn new concepts. As a classic example, Gentner 24 describes the use of the Bohr model to introduce atomic structure (target domain) by providing middle school students an analogy to the more familiar solar system (source analogy). Brown 25 emphasizes that analogic comparisons to concrete sources are most effective for stimulating conceptual change. These concrete comparisons allow students to attribute properties in the target domain to the entities in the source analogy, and work best when grounded in students' subconscious core intuitions. To illustrate with an example, de Almeida, Salvador and Costa 26 developed an analogic comparison of children in a school yard with the possibility of being given ice cream (source analogy) to help 9 th grade students understand the fundamental aspects of Drude's free electron model in metals (target domain). They report this concrete Page 26.375.3 comparison of a school yard helped students learn the associated concepts of electric current and EMF. Brown and Clement 27 further advocate the need for interactive learning environments rather than didactic presentation for the analogy strategy to be successful. However, the use of analogy is criticized by some because analogies can reinforce false associations between the target domain and the source, leading students to develop further misconceptions about target concepts. 28 Clement 21 includes four reasons that an analogy might not be successful in promoting conceptual change, including: insufficient understanding by the student of the source; the student cannot connect the source to the target (unable to map); the student might transfer too much from the source to the target (overmap); the source may not contain all the relations of the target concept. Methodology: Our study is designed to provide an empirical comparison of two activities that we have developed which correspond to each of Scott, Asoko and Driver's 12 groupings of effective reform teaching strategies: the cognitive conflict strategy and the analogy strategy. The learning environment is a studio classroom that is structured so students work in groups to interactively engage and make meaning of course content under facilitation and guidance from an instructor. 29 For each strategy, the learning tasks are directed through worksheets in the studios. We have done our best to carefully and thoughtfully develop the tasks. However, we acknowledge that there are many choices in task development and communication that influence student learning, and that the learning tasks can always be improved through observation and iteration. The results from our comparison of teaching strategies should be considered with this limitation in mind. Participants and setting All participants in this study were enrolled in a junior-level heat transfer course. It is the second course of a three-quarter Transport Phenomena sequence that is required for chemical engineering, bioengineering, and environmental engineering majors. The entire cohort met in one large group for traditional lecture twice a week (instead of recorded video) and was divided into six different studio class sections twice a week where the class was "flipped." Each week of the ten-week term, students engaged in the following sequence: lecture, studio, lecture, studio.