Curriculum References

This lesson aligns with the National Curriculum for England:

• Year 3 Number – Number and Place Value
• Year 3 Number – Addition and Subtraction

Specific learning objectives:

• Mentally add multiples of 10 to any 3-digit number, accurately crossing the next hundred where necessary (NC Year 3: Number – Addition and Subtraction).
• Use number bonds to 100 fluently to break down addition steps efficiently and flexibly (NC Year 3: Number – Number and Place Value).
• Identify changes in place value columns (hundreds, tens, ones) when adding multiples of 10 (NC Year 3: Number – Number and Place Value).

Prior Knowledge

• Number bonds to 10
• Counting in 1s and 10s
• Understanding of tens and ones columns
• Adding within the same tens boundary

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Learning Intentions

• LI1: Mentally add multiples of 10 to any 3-digit number, crossing the next hundred where necessary
• LI2: Use number bonds to 100 to break down addition steps fluently
• LI3: Identify and explain which place value columns change during the addition

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WILF (What I’m Looking For)

• Identifies next multiple of 10
• Partitions tens to bridge through a hundred
• Uses bridging method confidently to add multiples of 10
• Checks if answers are reasonable
• Uses key vocabulary orally and in written explanations

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Lesson Outline (60 minutes)

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1. Starter (10 minutes)

Objective

• Reinforce fluency in number bonds to 100 and partitioning within 100 to prepare for adding multiples of 10.

Activity

• Conduct a fast-paced oral and whiteboard quiz: Children work in pairs to answer questions like:
  • “70 + ? = 100”
  • “55 + ? = 100”
  • “30 + 40 = ?”
• Use a timer to build excitement and develop fluency.
• Recap the concept of “breaking numbers into parts to reach the next hundred.”

Formative Assessment

• Note who struggles with number bonds to 100 for targeted support.

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2. Introduction (10 minutes)

Objective

• Model adding multiples of 10 to 3-digit numbers and crossing hundreds mentally.

Teaching Input

• Use an interactive whiteboard and a place value chart to model the example:
  267 + 40
  • Partition 40 into 30 + 10.
  • Add 30 to reach 300, then add 10 to arrive at 310.
• Highlight which digits and place value columns change:
  • Ones digit remains the same.
  • Tens and hundreds digits may change when crossing hundreds.
• Emphasise language:
  • "I am adding 30 to move to the next hundred, then 10 more to complete."
• Link to mental strategies using partitioning and place value understanding.

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3. Guided Practice (15 minutes)

Objective

• Apply mental addition strategies flexibly to a variety of numbers.

Activity

• Provide whiteboards to each student.
• Give pairs sets of sums (multiples of 10 to add to 3-digit numbers), e.g.:
  • 284 + 50
  • 319 + 70
  • 485 + 60
• Ask pairs to explain their mental process aloud:
  • How did you choose to partition the tens?
  • Which columns changed and why?
• Teacher circulates, using prompts:
  • “How many more to get to the next hundred?”
  • “What is left to add afterward?”

Differentiation

• Support: prompt cards with sentence starters and worked examples.
• Challenge: encourage alternative mental routes or extension to multiples of 20 or 30.

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4. Independent Activity (15 minutes)

Objective

• Consolidate mental addition of multiples of 10 crossing hundreds.

Activity

• Worksheet with number sentences such as:
  • 346 + 50
  • 587 + 30
  • 699 + 20
• Children write down their mental steps explicitly:
  • How they partitioned the tens.
  • How they crossed hundreds.
• Encourage mental images or jottings rather than formal written methods only.

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5. Plenary (10 minutes)

Objective

• Reflect on understanding and articulate reasoning about addition strategies and place value.

Activity

• Facilitate a class discussion using questions:
  • “Which place value columns change when adding multiples of 10?”
  • “Why do we sometimes need to break tens into parts?”
  • “Who can explain how they worked out 267 + 40 mentally?”
• Use a quick ‘True or False’ quiz to recap:
  1. “Adding 30 always changes the hundreds digit.” (False – sometimes)
  2. “Adding 10 can change the hundreds digit if the tens digit is 9.” (True)
• Teacher assesses understanding through explanations and quiz responses.

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Extension and Support

Pupils needing support	Rapid graspers
Use Base 10 blocks for physical manipulation	Challenge to add multiples of 20, 30, or 100 mentally
Start with single additions without crossing	Explore alternative mental strategies and mental calculations with larger numbers

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Slide Deck Outline (For Interactive Whiteboard)

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Slide 1: Warm-Up: Number Bonds to 100

• Quick prompts: “70 + ? = 100”
• Pairs race format timer included

Slide 2: Adding Multiples of 10: Key Concept

• Example: 267 + 40
• Partition 40 into 30 and 10 visually on place value chart
• Highlight changing place value columns

Slide 3: Thinking Aloud: Mental Strategy

• Step 1: Add 30 to reach 300
• Step 2: Add 10 more
• Show notation: 267 + 30 = 300, 300 + 10 = 310

Slide 4: Guided Practice: Your Turn!

• List problems: 284 + 50 | 319 + 70 | 485 + 60
• Prompt: “How do you partition tens?” and “Which columns change?”
• Space for children to jot ideas on whiteboards

Slide 5: Independent Practice Instructions

• Worksheet problems, reminder to write mental steps
• Encouragement to use number bonds to 100

Slide 6: Plenary: True or False Quiz

• “Adding 30 always changes hundreds digit.”
• “Adding 10 changes hundreds digit if tens digit is 9.”
• Invite explanations

Slide 7: Vocabulary Check

• Partition | Multiple | Hundred | Tens | Ones | Mental Strategy
• Encourage children to use vocabulary in explanations

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Teacher Reflection Notes

• Watch for cognitive overload during starter and guided work; pause to model if many struggle.
• Encourage peer discussion and oral explanation for deeper understanding.
• Use formative assessment to plan future lessons on adding multiples of 100 or subtracting multiples of 10.

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This lesson plan supports a focused, progressive mastery of mental addition strategies aligned with the Year 3 National Curriculum. It embeds reasoning and fluency, supported by vocabulary development and opportunities for differentiated learning.