Addition and Subtraction Problem Solving

Grade: 2

Duration: 45 minutes

Class Size: 22 students

Curriculum Reference: Ontario Mathematics Curriculum, Grade 2 (2023)

Overall Expectation:
Use and apply mathematical processes to solve addition and subtraction problems.
Specific Expectations:
- 2NB01: Solve problems involving addition and subtraction of two-digit numbers, using concrete materials and drawings to represent the problems.
- 2NS01: Demonstrate mental math strategies to add and subtract numbers up to 100.
- 2MD05: Solve problems involving addition and subtraction in real-world contexts.

Learning Goals

Students will confidently solve addition and subtraction problems within 100 using a variety of strategies.
Students will demonstrate understanding by modelling problems with concrete materials, drawings, and mental math.
Students will explain their thinking clearly, using appropriate mathematical vocabulary.

Success Criteria

I can use objects and drawings to show addition and subtraction problems.
I can solve addition and subtraction questions in real-world contexts.
I can share my thinking and explain my problem-solving process.

Materials Needed

Base-10 blocks or counters (22 sets, one per student or pairs)
Whiteboards and markers
Problem-solving sheets with illustrated story problems (age-appropriate and contextually relevant)
Number lines (printed or drawn)
Timer or visual countdown clock
“Problem-solving hats” (paper hats or stickers to make problem-solving fun and special)

Learning Activities

1. Warm-up Activity (5 minutes)

Mental Math Sprint:
Teacher writes quick addition and subtraction facts on the board (e.g., 23 + 7, 56 – 9).
Students solve mentally and write answers on whiteboards.
Teacher randomly selects students to explain their mental strategy (e.g., counting on, making ten).
Ontario Focus: Developing mental math strategies (2NS01).

2. Introduction & Modelling (10 minutes)

Teacher presents a real-world story problem involving addition or subtraction within 100.
Example: "There are 38 apples in the basket, and the farmer picks 25 more. How many apples are there now?"
Teacher models solving it:
- Use base-10 blocks to represent the numbers.
- Draw a tens-and-ones place value chart.
- Demonstrate regrouping or combining using drawings.
Verbalize the problem-solving steps and encourage mathematical vocabulary: add, subtract, total, difference, regroup, tens, ones, etc.
Ontario Focus: Using concrete materials and drawings (2NB01).

3. Guided Practice & Exploration (15 minutes)

Students work in pairs (or individually if preferred) with base-10 blocks and problem-solving sheets featuring 3 story problems.
Problems designed with varying difficulty and contexts (e.g., classroom objects, animals, food) — meaningful and relatable to students’ lives.
Each student uses base-10 blocks or drawings to model the problem before writing their solution and explaining it to their partner.
Teacher circulates to support students, asking guiding questions to probe understanding and encourage different problem-solving strategies (e.g., “How did you break down the numbers?”, “What did you do if you needed to trade tens for ones?”).
Ontario Focus: Problem solving with manipulatives and peer communication (2MD05).

4. Class Sharing & Discussion (10 minutes)

Select 4-5 volunteers to share one problem they solved and explain their thinking using the “problem-solving hat.”
Encourage use of vocabulary and descriptive explanation.
Highlight different strategies observed in the class, e.g., using number lines, mental math, drawing pictures.
Discuss how sometimes more than one way can work to find the answer.
Reinforce respect for all ideas and collaborative learning.
Ontario Focus: Communicating mathematical thinking (2MD05).

5. Independent Application & Wrap-up (5 minutes)

Provide a short independent problem on a mini whiteboard or paper:
Example: "Maya had 47 stickers. She gave 19 to her friend. How many stickers does Maya have now?"
Students solve independently using their preferred strategy.
Teacher does a quick spot check or collects responses to gauge understanding.
Wrap-up by asking: "What was your favourite way to solve addition and subtraction today?" Encourage reflection and affirm effort.

Assessment for Learning

Observation of student use of concrete materials and drawings during hands-on work.
Listening to explanations for mathematical language and reasoning.
Review of independent problem for correctness and strategy use.
Teacher anecdotal notes to identify students needing extra support or challenge.

Differentiation Strategies

Support: Provide number lines or additional manipulatives, pair weaker students with stronger partners, use step-by-step guided questions.
Enrichment: Challenge advanced students to create their own story problems involving addition and subtraction or solve 3-digit numbers with the same strategies.
Use visual cues and consistent vocabulary to scaffold understanding.

Classroom Culture

Celebrate all attempts at problem-solving to build a growth mindset.
Use positive reinforcement and encourage peers to support one another.
Embed math talk as a daily routine and normalize sharing strategies.

Reflection for Next Lesson

Note which students need further practice with regrouping concept and mental math fluency.
Plan to incorporate technology next time (e.g., math apps or interactive games) for diversified engagement.

This lesson plan integrates Ontario’s curriculum expectations while fostering a lively, student-centred, hands-on approach to addition and subtraction problem solving that honours diverse strategies and nurtures mathematical communication.