Grade Level

Kindergarten - 2nd Grade (adaptations within lesson for age differences)

Duration

90 minutes

Unit Context

Unit: Mastering Math Concepts Together
Lesson Number: 2 of 17
Topic: Composing & Decomposing Numbers

---

Common Core State Standards Alignment

Kindergarten

CCSS.MATH.CONTENT.K.NBT.A.1

• Compose and decompose numbers from 11 to 19 into ten ones and some further ones.

1st Grade

CCSS.MATH.CONTENT.1.NBT.B.2

• Understand that the two digits of a two-digit number represent amounts of tens and ones.

2nd Grade

CCSS.MATH.CONTENT.2.NBT.A.1

• Understand that the three digits of a three-digit number represent amounts of hundreds, tens, and ones.

---

Learning Objectives

By the end of the lesson, students will be able to:

1. Explain what it means to compose and decompose numbers using tens and ones (Kindergarten/1st Grade) or hundreds, tens, and ones (2nd Grade).
2. Use visual aids (ten frames, base ten blocks, place value charts) to compose and decompose numbers within grade-level ranges.
3. Collaborate to create an anchor chart illustrating the steps and examples of composing and decomposing numbers.
4. Demonstrate understanding by decomposing given numbers and composing numbers from parts.
5. Communicate their mathematical thinking clearly to peers.

---

Materials Needed

• Base ten blocks (units, rods, flats) or alternative manipulatives
• Ten frames (printed or magnetic)
• Place value mats/chart
• Whiteboards and dry erase markers
• Paper, markers for anchor chart creation
• Number cards (11-99 for K-1, 100-999 for grade 2)
• Visual number puzzles (optional for enrichment)

---

Lesson Breakdown

1. Warm-Up: Number Sense Activation (10 minutes)

• Activity: Quick mental math game
• Say a number aloud (e.g., 24 for younger students, 135 for older)
• Students share how they might break the number apart orally (e.g., 20 + 4, or 100 + 30 + 5)
• Teacher briefly models the compositional thinking on the board
• Purpose: Engage prior knowledge and set the context for composing/decomposing

---

2. Direct Instruction: Concept Introduction (15 minutes)

• Explain the terms “compose” and “decompose” in child-friendly language:
  • Compose = putting parts together to make a whole
  • Decompose = breaking a whole into parts
• Use visual aids to model:
  • For K/1: Show 13 as 10 + 3 with ten frames and base ten blocks
  • For 2nd: Show 245 as 200 + 40 + 5 with base ten blocks (flats for hundred, rods for ten, units)
• Write number sentences corresponding to manipulative setups on the board

---

3. Guided Practice: Manipulatives & Visuals (25 minutes)

• Individual and Pair Work (3 students class):
• Provide each student with manipulatives and a place value mat
• Teacher calls out numbers fitting grade level, students compose & decompose physically (e.g., 17 → 10 + 7; 326 → 300 + 20 + 6)
• Students write number sentences on whiteboards
• Teacher circulates, supports, and asks probing questions:
  • “How many tens do you see?”
  • “What happens if you take apart this number into these parts?”
• Encourage students to explain their reasoning aloud

---

4. Anchor Chart Creation: Visual Summary (20 minutes)

• Collaborative Group Activity
• On a large chart paper or whiteboard, students contribute:
  • Definitions of compose and decompose in their own words
  • Visual models drawn or taped (pictures of base ten blocks, ten frames)
  • Number sentence examples with decompositions and compositions
• Teacher prompts with guiding questions:
  • “What pictures help you understand this?”
  • “How do you write it in numbers?”
• The chart will serve as a reference throughout the unit and can be displayed in the classroom or given as a handout copy for home use

---

5. Independent Application: Number Puzzles (15 minutes)

• Give students number cards and ask them to create 2-3 different ways to compose and decompose each number
• Encourage creativity with visuals—for example, “Can you break 58 down in two different ways?” (50+8 or 40+18)
• Students write or draw their answers and share out briefly with the group

---

6. Assessment & Reflection (5 minutes)

• Exit Ticket: On a small whiteboard or paper, each student must:
  • Decompose a given number (grade-appropriate) into parts using numbers or pictures
  • Compose a new number from given parts
• Teacher provides feedback and documents understanding
• Quick reflection: “What did you enjoy about composing or decomposing numbers today?”

---

Differentiation Strategies

• For Kindergarten and struggling students: Use concrete manipulatives heavily, stick to numbers 11-19, frequently use ten frames.
• For 2nd graders or advanced students: Introduce decomposition with three-digit numbers and explore alternative decompositions (e.g., 326 = 250 + 76).
• Provide sentence stems to support oral explanation (“I broke ____ into ____ and ___ because…”).
• Visual and tactile supports to assist diverse learners’ understanding.

---

Classroom Tips to Enhance Engagement & Impact

• Use bright colored base ten blocks and magnetic ten frames for hands-on appeal.
• Incorporate math storytelling: e.g., “Let’s help Bobby build number 34 by putting blocks together.”
• For anchor chart creation, assign each student a role (artist, scribe, designer) to encourage ownership.
• Record a short video segment (if tech allowed) of students explaining a decomposition to share with families.

---

End of Lesson

This lesson develops foundational place value understanding critical for arithmetic fluency and future math success, perfectly integrating Common Core standards with hands-on collaborative learning.