Subtracting Within 100

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Grade Level

2nd Grade

Duration

90 minutes

Class Size

14 students

Standards Addressed

• CCSS.MATH.CONTENT.2.NBT.B.5
  “Add and subtract within 100 using strategies based on place value and the relationship between addition and subtraction.”
• CCSS.MATH.CONTENT.2.OA.B.2
  “Fluently add and subtract within 20 using mental strategies...” (Supporting fluency in base operations)

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Learning Objectives

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

• Subtract a one-digit number from a two-digit number (where decomposing a ten is not required) using place value strategies and the inverse relationship of addition and subtraction.
• Explain their subtraction process using mathematical vocabulary such as addition, subtraction, altogether, more than, and less than.
• Collaborate with peers to solve subtraction problems in small groups.
• Demonstrate understanding through hands-on activities and written explanations.

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Materials Needed

• Base-ten blocks (ones and tens)
• Whiteboards and markers
• Subtraction task cards (problems like 65 - 23 without decomposing tens)
• Chart paper with vocabulary words and definitions
• Student math notebooks or writing paper
• Manipulative trays for center activities
• Number lines (large classroom version and individual copies)

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Lesson Breakdown

1. Warm-up and Review (10 minutes)

• Begin with a quick interactive group discussion to review subtraction facts within 20 (link to 2.OA.B.2 fluency).
• Use whiteboards: teacher says a subtraction fact (e.g., 17 - 8) and students write their answers.
• Introduce or review vocabulary: addition, subtraction, altogether, more than, less than on chart paper, with examples.

Purpose: Activate prior knowledge; reinforce fluency and vocabulary.

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2. Direct Instruction and Modeling (15 minutes)

• Explain the goal: subtract one-digit numbers from two-digit numbers without needing to break tens (e.g., 65 - 3).
• Use base-ten blocks to model subtraction with a number like 65 - 3:
  • Show 6 tens and 5 ones.
  • Remove 3 ones.
  • Count what remains (5 tens and 2 ones = 52).
• Write the problem vertically and horizontally on the board, modeling both formats.
• Connect subtraction to addition by asking:
  • If I subtract 3 from 65, what number plus 3 makes 65?
• Emphasize place value language and how it guides their thinking.

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3. Guided Practice in Whole Group (15 minutes)

• Present 4 subtraction problems on the board (e.g., 72 - 6, 58 - 4) with no decomposing tens.
• Use think-pair-share:
  • Students first solve individually with base-ten blocks or number lines.
  • Turn to a partner and explain their method using vocabulary words.
  • Share a few strategies aloud as a class.
• Teacher scaffolds as needed, asking guiding questions:
  • How many tens do you have? How many ones?
  • If you take away this many ones, what remains?

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4. Activity Centers: Differentiated Group Work (30 minutes total)

The class is divided into two small groups (7 students each), rotating between two centers every 15 minutes.

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Center 1: Hands-On Manipulative Play (Stage 1 / Emerging Skill Level)

• Students use base-ten blocks and number lines to solve subtraction problems from task cards focusing on numbers where ones can be easily subtracted without regrouping.
• Students record their answers and illustrate their work on whiteboards or paper.
• Teacher circulates, asking students to explain their thinking using the vocabulary words.
• Emphasis on concrete understanding and verbal explanation.

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Center 2: Partner Discussion and Writing (Stage 2 / Developing Skill Level)

• Students work in pairs with word problem cards involving subtraction of a one-digit number from a two-digit number (without decomposing tens).
• Each pair discusses the problem, solves it, and writes a short explanation in their math notebook including key vocabulary words.
• Example prompt:
  “Liam had 84 apples. He gave 5 apples to his friend. How many apples does Liam have now?”
• Teacher guides pairs to frame explanations clearly, modeling sentence starters like:
  • I subtracted ___ from ___ because...
  • The answer is ___ because...
• Pairs share a few solutions aloud for peer feedback.

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5. Class Discussion and Quick Check (10 minutes)

• Regather whole class. Select a few student pairs or individuals to share their problem-solving strategies and written explanations from centers.
• Use participation as formative assessment.
• Conduct a quick check: show 2 subtraction problems on the board, have students hold up fingers or mini whiteboards to show answers confidently and quickly.
• Ask comprehension questions focusing on vocabulary:
  • Which number is less?
  • Did we add or subtract? How do you know?

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6. Closing and Reflection (10 minutes)

• Recap the day’s lesson with a student-led vocabulary review on chart paper.
• Prompt students to reflect in notebooks:
  • What new strategy did you learn today?
  • Which subtraction problem was easiest/hardest? Why?
• End with a math story or quick game: “Tell me a subtraction story using a number from today’s problems.”
• Collect notebooks for review as evidence of learning.

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Evidence of Learning

• Completed hands-on activity work from Center 1 (student work samples with manipulative illustrations).
• Written explanations in math notebooks from Center 2 demonstrating understanding and use of vocabulary.
• Participation in class discussions and quick check responses.
• Teacher observation notes during guided practice and centers documenting student reasoning and vocabulary use.

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Differentiation / Scaffolding Strategies

• Provide number lines and manipulatives for students needing concrete supports.
• Use sentence starters and vocabulary prompts for students developing writing skills.
• Challenge advanced students by asking “What if” questions that extend problems slightly (e.g., “What happens if you subtract 7 instead of 3?”).
• Encourage peer tutoring in centers for collaborative learning.

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Classroom Management Tips

• Use clear visual and verbal signals for transitions between whole group and centers.
• Assign consistent partners/groups to foster collaborative rapport.
• Use praise and recognition for vocabulary use and participation to motivate learners.

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With this detailed, engaging, and standards-aligned lesson, your 2nd graders will confidently subtract one-digit numbers from two-digit numbers while building their foundational mathematical thinking and language skills.