Prime Numbers to 100
A comprehensive lesson teaching Year 5 students to identify and reason about prime numbers up to 100, distinguishing them from composite numbers using their knowledge of factors.
Learning objectives
- Identify prime numbers up to 100.
- Recall prime numbers up to 19.
- Distinguish between prime and composite numbers using factor pairs.
- Explain why 1 is not a prime number and why 2 is a unique prime.
Lesson plan (60 minutes)
Introduction · 10 min
Starter: 'Factor Finders'. Students list factors for numbers 1-10 on mini-whiteboards. Discuss which numbers have exactly two factors.
Development · 15 min
Teacher Explainer: Defining prime and composite numbers. Using the Sieve of Eratosthenes method to identify primes to 20.
Main Activity · 20 min
Differentiated Worksheet Activity: Students work through Support, Core, or Stretch tasks based on confidence.
Assessment · 10 min
Multiple Choice Quiz: A quick check for understanding to identify any lingering misconceptions.
Closing · 5 min
Plenary: Review the 'Is 1 a prime?' myth and summarize the uniqueness of the number 2.
Key vocabulary
- Prime Number
- A whole number greater than 1 that has exactly two factors (1 and itself).
- Composite Number
- A number that has more than two factors.
- Factor
- A number that divides into another number exactly without leaving a remainder.
- Factor Pair
- A list of two numbers that multiply together to make a product.
- Product
- The result of multiplying two or more numbers together.
Core worksheet (first questions)
- Write down all prime numbers less than 50.
- 'All prime numbers are odd.' Is this statement True or False? Explain.
- Is 15 a prime number? Prove your answer by listing all its factors.
- Find three prime numbers that are between 40 and 50.
Quiz (sample)
1. What is the definition of a prime number?
- A. A number that ends in 1, 3, 7, or 9.
- B. A number with exactly two factors: 1 and itself.
- C. Any odd number.
- D. A number that can be divided by 2.
2. Which of these is the only even prime number?
- A. 1
- B. 2
- C. 3
- D. 9
3. Why is the number 1 not considered a prime number?
- A. It is too small.
- B. It is an even number.
- C. It only has one factor (itself).
- D. It is a multiple of 3.
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