This lesson is optional, because it is an opportunity for extra practice that not all classes may need. In both activities, students have a choice between 2 centers introduced in previous lessons. Students choose the center they would like to participate in, and work with a partner on that activity. Use this lesson as an opportunity to establish structures for centers for the year, such as how materials will be organized, how many students will work at each center, how students will transition from one center to another, and how students will work together with partners at each center.