dents opportunities to clarify the question about moon phases, determine what would constitute evidence to support each explanation, model each of the alternative explanations, and then determine which explanation for moon phases is supported by the evidence they personally gathered earlier in the unit.

To assess what they already know before beginning the activity, Mr. Gilbert asks the students what they think their drawings should show. The students agree they should show: 1) the position of the earth and moon when looking down at the North Pole, 2) the source and path of sunlight using arrows and, 3) the shadows for the earth/globe and moon/balls. They also agree that the positions of earth and moon shadows are critical. With these consistent conditions in their drawings, it will be easier to compare findings and explanations for moon phases. Mr. Gilbert encourages them to show the moon in many different positions in its orbit around the earth.

Mr. Gilbert circulates among the groups, checking how they are setting up their materials and listening to the students’ conversations. He also makes sure to look at their drawings. From time to time he asks questions to probe students’ understandings and refocus their thinking about the relationship between evidence and explanation. “What moon shape would you see if the earth, sun, and moon were positioned as you have them now? Where would the moon have to be in your model to result in a quarter moon? Show me where the earth’s shadow would be. What evidence do you have that supports your conclusion or causes you to change your mind?” He asks students to show him the direction in which the moon moves around the earth in their model. Then he asks: “How do you know? What evidence led you to this conclusion?” When needed, Mr. Gilbert reminds students to look at the class data table: “A good model will explain the data.” Listening to student conversations and coaching with questions allows him to assess student progress in understanding the cause of moon phases. It also allows him to assess how well students are using certain inquiry abilities such as thinking critically and logically about the relationship between the evidence they gathered in earlier lessons and explanations.

Mr. Gilbert begins the next class by asking each group to post their model drawings and then invites the rest of the class to examine the results. Then Mr. Gilbert asks each group to describe their conclusions about the different explanations for moon phases. Their observations and interpretations seem to support the explanation that, as the moon moves in its orbit around the earth, the amount of the lighted side of the moon that can be seen from earth changes.

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