Math lesson plan · 6th grade (Year 7 in England) · 45 minutes
Tell prime numbers from composite numbers
Number sense
CCSS 4.OA.B.4England: Y5 Multiplication and divisionEngland: KS3 Number
Objective and success criteria
Students will: Tell prime numbers from composite numbers.
- I can answer questions on today's skill on my own, without help.
- I can explain each step and say why it works.
- I can check my answer and spot a mistake.
Before and after
Needs first: Test divisibility by 2, 3, 4, 5, 6, 9 and 10; Primes, squares and cubes
Leads to: the next skill in this area.
Materials: Place value chart, Base-ten blocks or a number line, Mini whiteboards and pens, Printed student sheet (below).
Warm-up · 5 min
- Quick retrieval from earlier learning (Test divisibility by 2, 3, 4, 5, 6, 9 and 10; Primes, squares and cubes). Students answer on mini whiteboards.
- Show answers together and note who needs support in the main task.
- Is 158 divisible by 2? (Yes / No) → YesPrompt: Test for 2: the last digit is even.
- 6³ = ? → 216Prompt: Cubed means three copies of the number multiplied together.
- Which number is divisible by 9? (693 / 346 / 295 / 254) → 693Prompt: Test for 9: the digit sum is a multiple of 9.
Hook · 5 min
- Show a number in the news or a price tag and ask what each digit is worth.
- Share the objective: Tell prime numbers from composite numbers. Read the success criteria together.
I do: model it · 10 min
- Work through the example out loud, saying why you do each step, not just what you do.
- Example: Is 61 prime or composite?
- Step 1: 61 has no factors except 1 and 61: prime.
- Answer: Prime
- Pause after each step and ask a student to say what comes next.
We do: guided practice · 10 min
- Do these together. Students try each step on whiteboards before you reveal it.
- Use the hints as prompts rather than giving the answer.
- Is 51 prime or composite? (Prime / Composite) → CompositePrompt: A prime number has exactly two factors: 1 and itself.
- Only one of these numbers is prime. Which one? (81 / 69 / 51 / 67) → 67Prompt: Odd numbers are not always prime. Test 3 (digit sum), 7 and 11.
You do: independent practice · 10 min
- Students work on the student sheet. Circulate and check the first two answers of every student early.
- Students who finish: write a question of their own for a partner, with the answer.
The 8 questions are on the student sheet below, with answers in the key.
Exit ticket · 5 min
- Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
- Only one of these numbers is prime. Which one? (101 / 93 / 63 / 57) → 101Prompt: Odd numbers are not always prime. Test 3 (digit sum), 7 and 11.
- How many prime numbers are there between 40 and 50? → 3Prompt: Even numbers (except 2) are never prime; nor are numbers ending in 5.
Watch out for
- Reading 1,045 as one thousand four hundred five: point to each place and say its value.
- Thinking a longer number is always bigger, even with decimals (0.45 vs 0.5).
Support and stretch
Support
- Review first: Test divisibility by 2, 3, 4, 5, 6, 9 and 10.
- Use concrete materials: place value chart.
- Give the first step of each question, or a partly worked example to finish.
- Pair with a confident partner for the guided practice.
Stretch
- Explain a common mistake in writing and how to fix it.
- Write a word problem that uses today's skill, then solve a partner's.
Homework and more practice
Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-6.
Free lesson plan from eurekami.com/lesson-plan-builder