Context: Grade 4, light study, whole class meeting.
S1: …If this room was totally black, the carpet would still be green… But you wouldn’t see it because there’s no light to bounce off of it, so you couldn’t see the color. Because it’s like a green light bounces off it so we can all see it…
Teacher: … I don’t understand why we’re talking about green light. I see a green carpet as we all say we do. But I see a white light, so how are we saying there’s green light here?
S2: Well if there was. [Students talk at once]…
S3: Um I’m just saying for you there is green light.
Teacher: In this room?
S3: Yep. [stands up, walks to the chalkboard, and draws a prism.] I just need… prism. You know how when you shine light through it, it makes the light split up into the…colors. [Pointing to the ceiling light] … that’s how the green light is there.
In this example, the teacher listened to S1′ “thought experiment” on what would happen to the green carpet if there were no light in the classroom. He picked up an important and challenging concept implied in S1’s talk: regular white light has colors in it. It was likely that this notion was not so clear to many of the students. Instead of stepping in to directly explain this concept, the teacher shared his problem and wondering: “I don’t understand…how are we saying there’s green light here?” This was followed by students’ active input to elaborate the nature of white light in relation to color vision.