Scott’s high school physics students were investigating how light interacts with different surfaces, such as a mirrors. While working with a laser and a mirror, the students became curious about how and why the light beam was visible when shined through fog but invisible when no fog was present. The video shows the subsequent class discussion about this phenomenon.

Focus Practices: Modeling (SEP2) and Questioning (SEP1)

We use this video case to show how the modeling and questioning practices were used by Scott and his students to explain this phenomenon. After learning about the lesson's context, we suggest you watch the clip at least two times: once to examine the modeling practice and a second time to examine the questioning practice. We have provided guiding questions and commentary for each practice.

Classroom Context Explained

This lesson occurs in the context of a broader unit in which students are constructing a model to account for the behaviors of waves (e.g. reflection, refraction, diffraction, etc.). Students are now considering whether light is an example of a wave.

Before this clip, the students explored how light reflected off of different surfaces. Scott then shined a laser onto a mirror to begin a planned discussion about how reflected light allows us to see images in mirrors. However, students became curious about why they could not see the laser beam, but they could see the spot on the mirror. In response, Scott used a fog machine to make the laser beam visible.  This prompted the students to ask why they could now see the light beam but could not before.  Although the students’ question diverged from the planned lesson, Scott recognized how pursuing it could deepen their understanding of light.

At this point, Scott asked students to use white boards to make their thinking visible. Students generated individual diagrams to answer the question, “How and why can we see the laser beam in the fog?”  This activity provided students the opportunity to make sense of the phenomenon on their own first. Scott then asked students to share their ideas with one another. One student, Steve, used his diagram to explain his explanation to the class.

Steve's Model
Steve's Diagram


Video - Teacher Describes the Lesson
Questions To Consider As You Watch

1. Why was it helpful for students to diagram their ideas before sharing their ideas with the class?
2. How could explaining the visible spot on the mirror be helpful for developing a light model?

1. What is the teacher's role in asking questions?
2. What is the relationship between asking questions and developing a model?

Video - Uninterrupted Classroom Activity
Connections between this Video and the Practices

Modeling in Context

What are models?
Although students might seek to explain specific situations, a goal of science is to identify general ideas, principles, or mechanisms that could be used to explain a range of situations.  These ideas can be synthesized into a coherent product called a scientific model that accounts for the relevant components, relationships, and underlying processes that lead to a phenomenon.

Understanding Steve’s Model
Steve identified the light bouncing off individual fog particles and entering our eyes as the mechanism by which we are able to observe the laser beam. Steve identified the components or parts of the phenomenon (“fog particles” and “beam of light”), the processes (“light bounces off of those particles”), and relationships between the parts that are relevant for explaining how and why they were able to see the laser beam. In addition, Steve showed evidence of applying general model ideas. For example, we know that light has to bounce off objects and enter our eyes for us to see them (“the ones [light beams] that bounce off – that's what we see”).  Steve acknowledged that some of the light did not reflect off the fog particles; instead that light traveled to and bounced off mirror.

Using Models to Explain Other Aspects of Phenomenon
One powerful use of models is their ability to explain other related situations.  This particular phenomenon provided multiple things to be explained.  Another student, James, observed a visible dot where the light beam interacted with the mirror.  He considered how Steve’s model could be used to explain this other aspect of the phenomenon.

In his explanation, James used three general ideas: 1) light reflects off objects in “perfect-V’s”, 2) light scatters off of “rough” surfaces, and 3) light has to bounce off objects and enter our eyes for us to be able to see them. However, because mirrors are “smooth” surfaces, he was confused as to how some of light could enter our eyes rather than having all of the light reflecting off the mirror and into the air.

To help students approach this new question, Scott asked the class whether the “spot on the mirror” phenomenon was similar to students’ ability to see a laser spot on a whiteboard.  By drawing their attention to another phenomenon, Scott leveraged the explanatory power of models and their ability to explain other related situations.

Erin explained that the students could see the dot on the mirror due to light reflecting and scattering off small imperfections on the mirror. Scott poked fun at her critique about his “imperfect” mirror, which is evidence of a classroom culture where students feel at ease to share ideas, critique their classmates, and ask questions.

Throughout this clip, we see evidence of students developing and using models – coherent sets of explanatory ideas that can explain observations in a range of phenomena. These model ideas involve the relevant components, relationships, and processes necessary for leading to the observations to be explained. Model ideas can be used to explain a range of related situations. Model ideas become more robust as they are used to explain a range of situations. Thus, when students encounter novel situations, the students can consider what they have encountered before that might be relevant for explaining the new situation.

Questioning in Context

The scientific endeavor is framed around posing and investigating questions about how the world works. There are different types of questions.  The first involves what students are trying to figure out: are students seeking to describe what is happening or are they trying to explain how and why the phenomenon is occurring. These types of questions make up the Practice of "Asking Questions" and are distinct from other types of questions one might ask in a classroom context such as those that elicit and clarify students’ ideas.

Understanding and Evaluating Steve’s Model
As Steve used his diagram to explain his ideas to his classmates, he was conscious about whether they understood his ideas (“Does that kind of make sense?”). Further, Scott invited students to formally ask questions about the presented ideas (“Anybody want to ask a question about what you see up there?”). In doing so, the students focused on evaluating the ideas (“what you see up there”) rather than critiquing the student.

How and why can we see the spot on the mirror?
James considered how Steve’s model could explain his ability to see the dot on the mirror. Thus, posing one question could motivate consideration of additional questions.

Shift in question framing student sensemaking
Because questions provide purpose for student sensemaking, it was important for the class to understand James’ question ("Let me just clarify... I think this is your question...") and make public the shift in what question was guiding the class and ask the students, rather than the teacher, to answer James’ question.

“Thumbs up. Thumbs down. Thumbs side ways.”
Scott asked the class whether they agreed with Erin’s explanation (“Does that make sense?  Thumbs up. Thumbs down. Thumbs sideways, you're not quite sure.”). This strategy provided a quick and low-risk way to assess students’ understanding of student ideas.

“I don’t understand what the question is…”
Sarah’s confusion involved unresolved issues with the first question involving how students could see the light beam.  Scott attempted to clarify his understanding of Sarah’s question, both verbally and using a diagram, yet was unsuccessful.  Another student, Erin, understood Sarah’s question. Thus, the responsibility for understanding and answering student questions does not always fall on the teacher. Sarah understood how students could see the light beam in the fog. However, she was confused about why all of light did scatter off the fog and result in cloud of light rather than a distinct beam. After clarifying Sarah’s question, the class discussed the fog’s density as a means to explain the observations.

The Teacher's Perspective

Watch the classroom video from Scott’s perspective as he explains his decisions and how he supported students' engagement in modeling and questioning to explain the phenomenon.

Video - The Teacher's Perspective
Video - The Next Steps