In this clip the teacher is having a discussion with a small group about what proportionality is and allows them to use the context of constant speed to explain.
Proportionality and Constant Speed, Clip 1, 1:46
The teacher is discussing proportionality in the context of constant speed, a context that is very familiar to students. This gives them something to relate to while trying to assimilate the defintion of proportionality.
One student makes the contribution that it is to "cover the same distance in the same amount of time." The teacher repeats this and makes sure everyone can hear.
The teacher then asks for another way to describe constant speed. This can allow for alternate ways of thinking to emerge in the classroom. Sine there is more than one way to describe constant speed, having more than one way be used in the classroom is very useful to students.
The teacher finishes by looking at some scaling examples to help them understand the topic.
