Add 9 Magic

Overview

Subject: Mathematics
Year Group: Year 3
Duration: 30 minutes
Number of Pupils: 1
Focus Strategy: Adding 9 using "add 10, take away 1"
Curriculum Area:
Primary National Curriculum (England) – Year 3 Mathematics
Number – Addition and Subtraction:

• Mental Maths: Add and subtract numbers mentally, including a three-digit number and ones
• Mathematical Thinking: Develop mental strategies using known number facts and place value

---

Learning Objective

By the end of the lesson, the pupil will be able to:

✔ Understand and apply the mental strategy of adding 9 by adding 10 and subtracting 1 (e.g. 27 + 9 → 27 + 10 = 37 → 37 - 1 = 36)
✔ Explain their thinking and justify their answers
✔ Begin to develop fluency using this strategy in varied contexts

---

Success Criteria

✅ I can add 9 by adding 10 and taking away 1
✅ I can show this strategy using objects, drawings, and number sentences
✅ I can explain how and why this strategy works

---

Resources

• Large number line (printed or drawn on paper/table)
• 20 counters (double-sided or two colours for visual contrast)
• Whiteboard and pen
• Mini whiteboard for pupil
• Laminated number cards (10–99)
• Sentence stem cards: "I added 10 to __, then I took away 1. My answer is __"
• Small mirror (used creatively in plenary)
• Post-it notes

---

Lesson Structure

🔍 1. Warm-Up (5 mins) – Number Aerobics!

A fun & physical starter to get the child engaged. Stand up with plenty of space.

Instructions:

• The teacher calls out two-digit numbers.
• The pupil must respond by adding 10 in their head and saying the answer aloud.
• Add a physical action: every time they hear a number ending with “9”, the pupil crouches into a “thinking pose” before answering.

E.g.:
Teacher: “34” → Pupil: “44” (stretch arms up)
Teacher: “48” → Pupil: “58” (jump in place)
Teacher: “29” → Pupil crouches: “39!”

Purpose: Practise quick mental addition of 10 while prompting awareness around numbers ending in 9.

---

👀 2. Discover the Trick (10 mins) – Let’s Investigate!

Approach: Use manipulatives to discover the “adding 9” shortcut step-by-step.

• Lay out a number line from 20–50.
• Use a counter to show 27 + 9.

First Try (Original strategy):

• Place a counter on 27.
• Count on 9 steps — slow, steady 1-to-1.
  Ask: “Was that quick or slow?”

Second Try (New strategy):

• Pupil places a counter on 27.
• Instead of counting 9 steps, jump 10 steps to 37.
• Then step back 1 → land on 36.
  Ask: “Was that faster? Did the number feel close?”
  Draw chimney sum together to confirm.

Visual Anchor:
Encourage the child to build a “math picture” by drawing it: a jump of 10, then back 1. Highlight the direction and efficiency.

Mathematical Talk Prompts:

• “What’s easier: 9 or 10?”
• “What happens if we do too much and then just take one away?”

Now repeat with additional numbers: try 34 + 9, 45 + 9 with number line and visual support.

---

🤹 3. Play it – Strategy in Action (10 mins)

Game: Mystery Number Detective!

“I’ll give you a clue. You need to find my mystery answer using our new shortcut!”

Set Up:

• Teacher holds up a card: “36 + 9”
• Pupil uses a mini-whiteboard to:
  • Show “add 10”
  • Take away 1
  • Reveal the answer
  • Read the full sentence: “I added 10 to 36 to get 46. Then I took away 1. My answer is 45.”

💡 Use the Sentence Stem Cards as support at first, gradually remove as confidence builds.

Extension Idea: Pupil creates their own number sentences to challenge the teacher! Reverse roles to develop metacognition.

---

🎭 4. Reflect & Wow (5 mins) – Talking Numbers + Magic Mirror

Show a small mirror to the pupil. Ask:

“Imagine you're a maths magician. How would you teach someone the shortcut for adding 9?”

Use the mirror symbolically: “When a mathematician looks in the mirror, they talk through their clever thinking!”
The pupil verbalises how to use the strategy using their own language and creativity.

Sentence prompt ideas for support:

• “When I see ___ + 9…”
• “I remember that I can…”
• “I feel confident because…”

Stick a Post-it Note with their "magic tip" on the learning wall/book to celebrate their learning!

---

Assessment Opportunities

• Observe confidence and speed in mental calculations
• Note when pupil shifts from 1-to-1 counting to strategy-based thinking
• Listen for accurate use of maths vocabulary and strategy explanation
• Use pupil-created examples to assess depth of understanding

---

Differentiation & Support

• Use number lines and counters for additional scaffolding
• Offer stem sentences for verbal explanations
• Challenge by introducing 3-digit numbers: 173 + 9
• For EAL: Pair number visuals with icons and actions

---

Cross-Curricular Sparks

• Drama/Narrative: Invent a Maths Magician character who uses 'add 10, take away 1' as their superpower
• Art: Create number jump trails showing 10 up, 1 back using your favourite colours

---

Teacher Reflection

• Did the pupil shift from counting in ones to using the derived fact strategy?
• Were they able to verbalise and visualise the process confidently?
• Did the pupil enjoy the learning? What part sparked the most excitement?

Next Step Suggestion: Introduce subtracting 9 using a similar technique (subtract 10, add 1), building from what they now know.

---

🪄 Let’s turn numbers into magic – helping children see maths is not just about the answer, but about clever thinking!

---

Prepared with creativity and rigour for the curious minds of Year 3 😃