Objective: Students will learn to add by counting on from the larger number.
Materials: Number line, counters, worksheets
Activity: Demonstrate with 8 + 3 by starting at 8 and counting on 3 more: 9, 10, 11.
Practice: 7 + 4, 9 + 2, 6 + 5
Assessment: Students solve 5 addition problems independently.
Objective: Students will learn to make ten when adding numbers close to 10.
Materials: Ten frames, counters, manipulatives
Activity: Show 9 + 4 as 9 + 1 + 3 = 10 + 3 = 13.
Practice: 8 + 5, 7 + 4, 6 + 6
Assessment: Students demonstrate making ten with manipulatives.
Objective: Students will use doubles facts to solve near doubles problems.
Materials: Dice, dominoes, flashcards
Activity: Review doubles (5 + 5 = 10) and near doubles (5 + 6 = 11).
Practice: 4 + 4, 4 + 5, 7 + 7, 7 + 8
Assessment: Students complete doubles and near doubles worksheet.
Objective: Students will learn to subtract by counting back from the larger number.
Materials: Number line, counters, worksheets
Activity: Demonstrate with 12 - 3 by starting at 12 and counting back: 11, 10, 9.
Practice: 15 - 4, 11 - 2, 13 - 5
Assessment: Students solve 5 subtraction problems independently.
Objective: Students will use addition facts to solve subtraction problems.
Materials: Fact family triangles, worksheets
Activity: Show 15 - 8 by thinking "What plus 8 equals 15?" Answer: 7.
Practice: 14 - 6, 16 - 9, 13 - 7
Assessment: Students explain their thinking for solving subtraction problems.
Objective: Students will practice both addition and subtraction within 20.
Materials: Mixed operation worksheets, games, manipulatives
Activity: Math centers with addition and subtraction games.
Practice: Mixed problems: 8 + 7, 15 - 8, 9 + 6, 14 - 5
Assessment: Comprehensive quiz on adding and subtracting within 20.
Adding & Subtracting Within 20
Strategies and Methods
Addition
Subtraction
Practice Makes Perfect!
This section provides a comprehensive overview of adding and subtracting within 20, including definitions, methods, strategies, and key concepts for 1st grade students.
Addition: Combining numbers to find a total or sum.
Subtraction: Taking away one number from another to find the difference.
Within 20: Problems where the answer is 20 or less.
Number Sense: Understanding relationships between numbers.
• Addition and subtraction are inverse operations
• Order matters in subtraction but not addition
• Use strategies to solve mentally
• Check answers by using the opposite operation
Counting On: Start with the larger number and count up
Making Ten: Break apart numbers to make 10
Doubles: Use known doubles facts
Near Doubles: Adjust doubles facts slightly
Counting Back: Start with the larger number and count down
Think Addition: Use addition facts to solve subtraction
Fact Families: Use related addition and subtraction facts
Number Line: Move backward on the number line
Addition: 8 + 5 = 13 (count on: 8, 9, 10, 11, 12, 13)
Subtraction: 13 - 5 = 8 (think: 5 + ? = 13)
Making Ten: 9 + 4 = 9 + 1 + 3 = 10 + 3 = 13
Fact Family: 7 + 8 = 15, 8 + 7 = 15, 15 - 7 = 8, 15 - 8 = 7
• Start with the larger number when adding
• Use fingers or drawings if needed
• Practice doubles facts regularly
• Check answers by using the opposite operation
Questions & Answers
Question: What are the most effective strategies for teaching addition and subtraction within 20 to 1st graders?
Answer: The most effective strategies for 1st graders include:
- Concrete Manipulatives: Use counters, cubes, or other physical objects to represent numbers.
- Number Lines: Help students visualize addition as moving forward and subtraction as moving backward.
- Ten Frames: Develop number sense and help students see relationships to 10.
- Counting Strategies: Counting on for addition and counting back for subtraction.
- Fact Families: Connect addition and subtraction to show inverse relationships.
Start with concrete materials, then move to pictorial representations, and finally abstract symbols. This progression supports conceptual understanding.
Focus on strategies rather than rote memorization, especially in early lessons.
Question: My child is struggling with subtraction within 20. They seem to understand addition but get confused with subtraction. Any suggestions?
Answer: This is very common! Try these approaches:
- Think Addition Strategy: For 14 - 8, think "What plus 8 equals 14?"
- Use Known Facts: If they know 8 + 6 = 14, then 14 - 8 = 6
- Count Up: For 14 - 8, count up from 8 to 14: 9, 10, 11, 12, 13, 14 (that's 6 numbers)
- Number Line: Start at 14 and jump back 8 spaces
- Fact Families: Practice sets like 6 + 8 = 14, 8 + 6 = 14, 14 - 6 = 8, 14 - 8 = 6
Emphasize that subtraction is the opposite of addition. Practice fact families together to strengthen the connection between operations.
Be patient - subtraction often takes longer to master than addition.
Question: How can I get faster at adding and subtracting within 20? Sometimes I count on my fingers and it takes too long.
Answer: Great question! Here are ways to get faster:
- Learn Doubles First: 2+2, 3+3, 4+4, etc. These are easy to remember!
- Practice Near Doubles: If you know 5+5=10, then 5+6=11
- Make Ten: For 8+6, think 8+2=10, then add the remaining 4 to get 14
- Memorize Key Facts: Focus on facts that come up often
- Play Math Games: Fun practice helps with memorization
Start with strategies that make sense to you, then practice them over and over. Soon they'll become automatic!
It's okay to use fingers at first - that's how we learn! But with practice, you'll be able to do more in your head.
Try practicing for just 5-10 minutes each day to build fluency.