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Productive prior knowledge

November 30, 2012

Today in journal club we were talking about eliciting students’ prior knowledge and using that knowledge to inform instruction. Randi brought up moon phases and how every semester a large number of students suggest that moon phases are caused by the Earth’s shadow. We started talking about what is productive in this idea.

I suggested that the shadow hypothesis makes use of the idea that if light from the sun does not strike a certain part of the moon then that part of the moon will appear dark. This is a correct idea and an important part of accurately explaining the moon phases. I claimed that the only error in the shadow hypothesis is that the part of the moon that is dark is not due to something blocking the sun’s light.

Randi went further to say that actually there is something blocking the sun’s light. The moon. At any moment, half of the moon (referring to the entire sphere) is dark because the other half of the moon is blocking the sun’s light.

All of the sudden the shadow hypothesis, which originally sounded like a serious misconception, sounds pretty close to the correct explanation. This is not to suggest that building the mental model of the moon orbiting around the earth and using this model to predict when different phases will occur is easy. Certainly there is still some heavy cognitive lifting separating the shadow hypothesis from the correct scientific explanation. But I was surprised by how quickly we were able to find significant and accurate mechanistic reasoning in the shadow hypothesis.

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From → Resources, Teaching

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