# Lesson 4

### Lesson Purpose

The purpose of this lesson is for students to use their knowledge of base-ten diagrams to make sense of two written addition algorithms.

### Lesson Narrative

In a previous lesson, students revisited addition within 1,000 using strategies based on place value, and properties of operations. An algorithm is different from a strategy because it is a set of steps that works every time as long as the steps are carried out correctly. The algorithms introduced in this lesson draw on the grade 2 work within 1,000 in that they show the addition of ones to ones, tens to tens, and hundreds to hundreds. Students should have access to base-ten blocks if they choose to use them.

• Engagement
• MLR7

Activity 1: What is an Algorithm?

### Learning Goals

Teacher Facing

• Relate base-ten diagrams to written algorithms for addition.

### Student Facing

• Let’s learn new ways to add.

### Required Materials

Materials to Gather

### Lesson Timeline

 Warm-up 10 min Activity 1 20 min Activity 2 15 min Lesson Synthesis 10 min Cool-down 5 min

### Teacher Reflection Questions

In grade 2, students spent significant time working with place value. How did students’ work with place value prepare them for the move to using algorithms to add?

### Suggested Centers

• Target Numbers (1–5), Stage 6: Add Hundreds, Tens, or Ones (Addressing)
• Five in a Row: Addition and Subtraction (1–2), Stage 8: Add within 1,000 with Composing (Addressing)
• Rectangle Rumble (3–5), Stage 2: Factors 1–5 (Supporting)