In this lesson, students practice explaining their methods for adding two-digit numbers based on place value and the properties of operations (MP3). In the first activity, students are invited to choose any method that makes sense to them to add within 100 and explain their method to their peers. In the second activity, students use what they have learned about place value and methods for adding to create expressions that meet different constraints. Throughout the lesson, monitor for ways students are reasoning about place value and the structure of numbers (MP7).

Activity 3 is an optional activity that offers practice adding within 100 in real-world contexts.

This lesson has a Student Section Summary.

As you finish up this unit, reflect on the norms and activities that have supported each student in learning math. How have you seen each student grow as a young mathematician throughout this work? How have you seen yourself grow as a teacher? What will you continue to do and what will you improve on in Unit 6?