The lesson opens with the teacher connecting the work students will engage with in this lesson to work done in previous grades and lesson.  By having students create a description of a rectangle, the teacher is able to access where students' understanding is with previous content.

Here, the teacher poses two high-quality questions.  Even though students only work on two questions throughout the class, students are encouraged to communicate their thinking with a table-mate or the teacher. 

Here, students are given extensive time to work with course-level problems.  As the students are working, the teacher walks around to check-in with groups.  While working with groups, the teacher asks students to explain and justify work and provides feedback that helps students revise initial work.

Throughout the lesson, most students talk about and question each other's thinking in order to strengthen their own understanding of the problem.  In this part of the lesson, you can hear the group in the center of the room talk about the problem and how they worked it in order to clarify their understanding of the concept. 

In this part of the lesson, a student works a problem on the board and explains his reasoning to the entire class.  The teacher poses specific questions that allows the student to elaborate with a second sentence to explain his thinking.  While doing so, the student realizes he needed to use an extra step using a reflexive.