Mathematics · Grade 2

Active learning ideas

Adding and Subtracting within 200

Active learning works especially well for adding and subtracting within 200 because it lets students physically manipulate place value and visualize number relationships. Concrete tools like base-10 blocks and open number lines turn abstract procedures into visible, repeatable steps that build both accuracy and confidence.

• Ontario Curriculum Expectations
• 2.NBT.B.7

• 20–40 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Think-Pair-Share
• 25 min · Pairs

Pairs: Number Line Jumps

Partners solve five addition or subtraction problems within 200 using open number lines, jumping tens first then ones. They label jumps and explain reasoning to each other. Verify answers with quick sketches or counters.

How are the steps for adding three-digit numbers similar to adding two-digit numbers?

Facilitation Tip

During Pairs: Number Line Jumps, circulate and ask guiding questions like ‘Which jump feels most efficient here?’ to push students beyond counting by ones.

What to look for

Present students with a problem like 135 + 42. Ask them to solve it using base-ten blocks or a drawing, and then write one sentence explaining their strategy. Check for accurate calculation and clear explanation of their chosen method.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 02

• Think-Pair-Share
• 40 min · Small Groups

Small Groups: Place Value Stations

Prepare three stations with base-10 blocks, hundreds charts, and drawings. Groups solve the same three problems at each, recording strategies used. Rotate stations, then share one insight per group.

Can you use an open number line to solve 126 + 45?

Facilitation Tip

During Small Groups: Place Value Stations, rotate to each group to prompt with ‘Trade your ten ones—how many tens do you have now?’ to reinforce regrouping.

What to look for

Pose the question: 'How is solving 150 - 30 different from solving 150 - 27?' Facilitate a class discussion where students compare the strategies, focusing on whether regrouping is needed and how the open number line might be used differently for each problem.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 03

• Think-Pair-Share
• 30 min · Whole Class

Whole Class: Strategy Showdown

Pose a problem like 183 - 50. Students solve individually with preferred tools, pair to compare methods, then present top strategies to class for vote on most efficient.

What strategy would you use to solve 183 − 50?

Facilitation Tip

During Whole Class: Strategy Showdown, invite students to share their drawings or number lines so peers can compare approaches and learn from each other.

What to look for

Give each student an exit ticket with the problem 182 - 50. Ask them to solve it using an open number line and to write down the jumps they made. Collect and review the tickets to assess their understanding of subtraction strategies on a number line.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 04

• Think-Pair-Share
• 20 min · Individual

Individual: Model Match-Up

Provide problems and strategy cards (blocks, line, drawing). Students pick a problem, match two models, solve both ways, and note which feels fastest in journals.

How are the steps for adding three-digit numbers similar to adding two-digit numbers?

Facilitation Tip

During Individual: Model Match-Up, watch for students who skip the written record; prompt them to trace their steps on paper to build accountability.

What to look for

Present students with a problem like 135 + 42. Ask them to solve it using base-ten blocks or a drawing, and then write one sentence explaining their strategy. Check for accurate calculation and clear explanation of their chosen method.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

A few notes on teaching this unit

Experienced teachers teach this topic by anchoring everything in place value first, using base-10 blocks to make regrouping visible before moving to drawings or symbols. They avoid rushing to the algorithm and instead encourage students to verbalize their thinking, often writing it down as they go. Research shows that students who practice mental math through number lines and decomposition develop stronger number sense than those who rely solely on column methods.

Successful learning looks like students selecting flexible strategies based on the numbers, explaining their thinking clearly, and moving between concrete models and mental math with ease. You’ll see them decompose numbers, regroup intentionally, and use number lines efficiently to solve problems like 145 + 67 or 178 - 43.

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Watch Out for These Misconceptions

• During Pairs: Number Line Jumps, watch for students who always start from zero or make tiny ones jumps even when tens are efficient.

  Redirect by asking ‘Can you start at the bigger number and jump tens first?’ and model a jump of 50 or 20 to show how it speeds up the process.

• During Small Groups: Place Value Stations, watch for students who regroup without trading ten ones for a ten, just moving blocks around loosely.

  Have them recount aloud while physically trading blocks, saying ‘Ten ones make one ten’ to reinforce the place value rule.

• During Whole Class: Strategy Showdown, watch for students who insist subtraction always means ‘take away’ and count back by ones regardless of the numbers.

  Introduce a subtraction problem like 185 - 50 and ask the class to brainstorm ways to subtract 50 without counting down by ones.

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Methods used in this brief

• Think-Pair-Share