Subject

Mathematics

Learning Objective

Students will represent addition and subtraction problems on a number line using place value strategies for sums and differences within 100 that do not require decomposing a ten.

Learning Standards

• 2.NBT.B.5: Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
• 2.MD.B.6: Represent whole numbers on a number line diagram.

Key Vocabulary

• Number line
• Place value
• Tens
• Ones
• Addition
• Subtraction
• Sum
• Difference

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Lesson Timeline (90 minutes)

Hook (Launch, Warm-Up) — 10 minutes

Activity:

1. Begin with a quick oral number line game. Prepare a large number line (0-120) on the floor or a chart. Call out simple additions and subtractions without regrouping that the students solve by physically hopping along the number line (e.g., "Start at 23, add 5").
2. Engage students by asking: "How did you decide where to jump on the number line? What helped you know the answer so quickly?"
3. Connect their strategies with place value language.

Purpose: Activate prior knowledge of number lines and addition/subtraction.

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Learn (Explore)

Mini-lesson (I Do) — 15 minutes

Objective: Model solving addition and subtraction problems using place value on a number line, focusing on tens and ones without decomposing a ten.

Steps:

• Display a number line from 0-100 on the board or projector.
• Select a problem like 42 + 33. Annotate “42” on the number line.
• Show how to add the tens first (+30), marking jump from 42 to 72.
• Then add the ones (+3), jumping from 72 to 75.
• Explain the process verbally, emphasizing tens and ones, not breaking apart (decomposing) a ten.
• Repeat with a subtraction problem such as 65 - 24, moving backward first by tens (-20) then ones (-4).

Use color-coded markers or highlighting to show the tens and ones jumps clearly on the number line.

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Guided Practice (We Do) — 20 minutes

Activity:

• Distribute small whiteboards and number lines to students or use paper strips with number lines 0–100.
• Provide 3-4 problems (addition and subtraction without decomposing tens).
• Conduct a think-aloud and complete the first two problems together as a class.
• Prompt students to label tens and ones jumps and verbally explain their reasoning.
• Encourage pairs to solve the last few problems with teacher support.

Example problems:

• 54 + 25
• 81 - 12
• 37 + 42
• 90 - 35

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Independent Practice (You Do) — 25 minutes

Activity:

• Provide a worksheet with number lines and 6 addition and subtraction problems within 100 that students solve individually.
• Instructions: Use the number line to add or subtract by tens first, then ones. Label each jump and write the final answer.
• Problems will avoid decomposing tens (e.g., 23 + 44, 68 - 27).
• Circulate to support and ensure understanding.

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Closing (Synthesis, Discuss) — 10 minutes

Activity:

• Gather students and have a short discussion:
  • “How does breaking apart numbers into tens and ones help us with addition and subtraction?”
  • “Why is the number line helpful? How can it show the steps clearly?”
• Invite 2-3 students to share their method and explain their number line strategy.
• Highlight how using place value on a number line helps organize thinking and visualize calculations.

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Fluency Focus

• Daily 5-minute quick drills on addition and subtraction within 100 using mental math or number line drawings.
• Emphasize jumping by tens and then by ones for speed and accuracy.

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Differentiation

Group	Strategy
Struggling	Use smaller numbers (within 50), provide a number line with marked tens, and one-on-one support.
On-Level	Work with numbers within 100 without decomposing tens, scaffolded guided practice and independent tasks.
Advanced	Challenge with open-ended problems to create their own addition/subtraction story problems using number lines.

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Assessment

Cool Down:

• Quick exit slip with 2 addition/subtraction problems on a blank number line (e.g., 45 + 23, 77 - 34). Students draw jumps and write answers.

Formative:

• Observation during guided and independent practice of correct place value jumps on number lines and accurate sums/differences.

Summative (Optional for End of Unit):

• A quiz including problems requiring number line strategies and explanation of using place value.

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This lesson plan ensures a balance of direct instruction, hands-on practice, visualization, and language development, perfectly aligning with CCSS Standards 2.NBT.B.5 and 2.MD.B.6 for 2nd grade mathematics.