This lesson is optional because it is an opportunity for extra practice interpreting diagrams and adding and subtracting within 100 that not all classes may need. In the first activity, students learn Stage 5 of the Math Stories center, which was last introduced in grade 1. In this new stage, called Tape Diagrams, students interpret tape diagrams and create their own story problems to solve. Then students choose a center based on what they need to practice. Students may continue to choose stages that provide additional practice adding and subtracting two-digit numbers, or they may choose the stages that provide fluency practice with addition and subtraction within 20.

As needed, revisit and reinforce the structures and norms for centers that were established in previous lessons.

As you finish up this unit, reflect on the norms and activities that have supported each student in learning math. List ways you have seen each student grow as a young mathematician throughout this work. List ways you have seen yourself grow as a teacher. What will you continue to do and what will you improve upon in the next unit?