Subtraction Strategies Uncovered

Subject: Mathematics

Grade: 2nd Grade
Duration: 90 minutes
Class Size: 14 students

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Learning Objective

Students will be able to describe and compare different methods of subtracting a one-digit number from a two-digit number within 100, using place value concepts and the relationship between addition and subtraction. They will understand how the methods are similar and different when solving problems like 65 – 23, without decomposing tens.

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Learning Standards

• Common Core State Standards: 2.NBT.B.5
  Add and subtract within 100 using strategies based on place value and the relationship between addition and subtraction.

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Key Vocabulary

• Subtraction
• Place value
• Tens
• Ones
• Difference
• Add
• Altogether
• More than
• Less than
• Method
• Strategy

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Materials Needed

• Base-ten blocks (tens rods and ones units)
• Whiteboards and dry erase markers
• Subtraction strategy anchor chart
• Printable subtraction problem cards
• Place value mats
• Journals or math notebooks
• Pencil and eraser

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Lesson Breakdown

Hook (Launch – Warm-up) – 10 minutes

Activity: Number Story Circle

• Begin by telling a subtraction story that involves a two-digit number minus a one-digit number (e.g., "Sally had 45 stickers, she gave 7 to her friend. How many does she have left?").
• Invite several students to share their own subtraction stories involving similar numbers aloud.
• Record select stories on the board, highlighting subtraction terms like “less than” or “difference”.
• Introduce today’s question: How can we subtract a one-digit number from a two-digit number? What strategies can we use?
• Engage the class in a brief discussion on any strategies they already know.

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Learn (Explore)

Mini-lesson (I Do) – 15 minutes

Focus: Demonstrate two subtraction methods

• Method 1: Counting Back on Number Line
  • Using a large classroom number line, model subtracting a one-digit number from a two-digit number by counting backward (e.g., start at 65, count back 3).
• Method 2: Place Value Decomposition without Borrowing
  • Use base-ten blocks to model the subtraction (e.g., 65 - 23).
  • Show how to subtract tens from tens and ones from ones without breaking apart any ten rods in these problems.
• Use a visual anchor chart to show the steps, emphasizing place value and place-by-place subtraction.
• Verbalize thinking to focus on similarities and differences of the methods (counting vs. place value).

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Guided Practice (We Do) – 20 minutes

Activity: Small Group Centers (Groups of 7, 2 groups total)

• Center 1 (Stage 3) - Using base-ten blocks and place value mats, students will solve subtraction problems like 54 - 21, focusing on decomposing tens only if the problem requires (for this lesson, decomposing isn’t required).
• Prompt students to explain their steps aloud to partners.
• Center 2 (Stage 4) - Use number lines and whiteboards to practice counting backward for 1-digit subtractions from two-digit numbers (e.g., 68 - 4).
• Teacher rotates between groups providing scaffolding — asking probing questions like, “What are you subtracting first?” and “How is this like or different from the other method?”
• Record students’ observations about method similarities and differences in their math notebooks.

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Independent Practice (You Do) – 20 minutes

Activity: Problem Solving & Strategy Comparison

• Each student receives a worksheet with a series of subtraction problems (e.g., 72 - 5, 46 - 2, 63 - 3).
• Students solve each using both methods:
  1. Counting backward on their personal number lines or with drawing hops.
  2. Subtracting by place value using base-ten representations on paper or drawings.
• Students write a short reflection (1-2 sentences) describing how the two methods are alike and different based on their experience.
• Teacher offers support to any student who struggles by suggesting re-visiting the hands-on materials.

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Closing (Synthesis, Discuss) – 10 minutes

• Gather whole class for a discussion. Invite 3-4 students to share their reflections aloud.
• Display the subtraction strategy anchor chart and invite students to tell key takeaways.
• Highlight how knowing multiple methods helps in different situations.
• Say a final guiding question: Which method do you like best and why?
• Reinforce vocabulary and importance of understanding place value in subtraction.

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Fluency Focus – Throughout Lesson

• Encourage quick oral counting backward during transitions and warm-up games.
• Incorporate “flash” subtraction facts for quick recall (e.g., subtracting 1-9 from numbers under 100).
• Use simple math chants to reinforce subtraction terminology.

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Differentiation

• For learners needing support: Provide additional one-on-one time with base-ten blocks; use simpler numbers closer to 30-50 to build confidence.
• For advanced learners: Challenge them with higher two-digit subtraction problems that require decomposing tens (not the main focus but extension).
• Use peer tutoring to support collaborative learning and scaffolding within small groups.
• Visual aids such as number lines and place value mats support multiple learning styles.

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Assessment

Evidence of Learning:

• Written subtraction problems completed independently, showing both strategies.
• Reflection sentences in math journals describing method differences and similarities.
• Participation in group discussions and explanations during guided activities.
• Ongoing formative assessment through teacher observation and questioning during centers.

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This lesson addresses Common Core Standard 2.NBT.B.5 fully by engaging students in multiple, place value-based strategies for subtraction within 100 and emphasizing conceptual understanding through active learning and collaborative discussions.