Prime Numbers Teacher Guide Prime Number Detectives
Teacher Facilitation Guide
Total Time: 35 Minutes
Learning Objective
Students will differentiate between prime and composite numbers by identifying factors and using a sieve-based filtering method.
Key Vocabulary
Prime Number: Only 2 factors (1 & itself)Composite Number: More than 2 factorsFactors: Numbers multiplied togetherFactor Tree: Visual diagram for factors
Materials
Factor Forest Slides
Prime Sieve Worksheet (1 per student)
Prime Proof Exit Ticket
Colored pencils/highlighters
Lesson Sequence
5 min
Warm-Up: Factor Hunters
Ask students to find all multiplication equations for the number 6 (1x6, 2x3). Then do the same for 5 (1x5 only).
"Class, why does 6 have more 'hunters' finding pairs than 5? Today we're giving these two types of numbers names: Prime and Composite."
5 min
Video: How to Factor Prime Numbers
Watch from 0:00 to 2:00. Use these pause points:
1:15 - Ask: "Why do you think it's called a 'Factor Tree'?"1:23 - Pause on the list. Ask: "What do you notice about all these numbers except 2?" (They are all odd).
20 min
Main Activity: Prime Sieve Challenge
Distribute the 1-50 grid worksheet.
Students circle the primes listed in the video (2, 3, 5, 7, 11, etc.)
Challenge: Test remaining numbers. If they find *any* factors other than 1 and itself, mark it "Composite" with an X.
Focus on "tricky" numbers like 9, 15, and 21 (odd but composite).
5 min
Closure: Prime Proof
Hand out Exit Tickets. Students identify if 9 is prime or composite and draw an array or factor tree to prove it.
Common Misconception
Students often think all odd numbers are prime. Highlight 9 (3x3), 15 (3x5), and 21 (3x7) as examples of odd composite numbers.
The "1" Rule
Explain that 1 is a special number—it is neither prime nor composite because it only has one factor (itself).
Prime Detective Slides Prime Number Detectives
Cracking the code of factors!
Factor Hunters
5 Minutes
6
How many ways can you multiply to make 6?
1 × 6 = 6
2 × 3 = 6
5
How many ways can you multiply to make 5?
1 × 5 = 5
The Big Reveal
P Prime Number
A number that can ONLY be divided by 1 and itself .
Example: 5
Factors: 1, 5
C Composite Number
A number that has more than two factors.
Example: 6
Factors: 1, 2, 3, 6
Is 1 special? Yes! 1 is neither prime nor composite!
Mission Briefing
Watch: 0:00 - 2:00
Embedded media
Pause @ 1:15
Why do you think it is called a "Factor Tree"?
Pause @ 1:23
What is the only even prime number on the list?
The Prime Sieve Challenge
1
Circle the Prime Numbers from the video list on your grid.
2
Hunt for factors in the other numbers. Can you find ANY other multiplication pairs?
3
If you find a new factor, cross it out with an X ! It is Composite!
Watch Out!
"Some odd numbers are tricky. Just because it is odd doesn't mean it is prime! Check 9, 15, and 21!"
Prime Sieve Worksheet Prime Sieve Challenge
Hunt for the factors of 1-50!
Name:
Date:
Part 1: Factor Hunters
Find all the factors of 6:
Find all the factors of 5:
Part 2: The Sieve (1-50)
Circle Primes
Cross out Composites
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Part 3: Testing the Odds
Pick a number from the grid that you marked as Composite (X). Prove it below by finding at least one factor pair other than 1 and itself.
Number I am testing:
Factors I found:
Remember: Prime numbers have only two factors. Composite numbers have more!
Prime Proof Exit Ticket Proof of Prime
Exit Ticket • Level 4 Math
Detective Name
Date
Case Number: 9
Is the number 9 Prime or Composite?
Prime
Composite
Show Your Evidence
Draw a picture (like a factor tree or an array) to prove your answer.
The Verdict
"I know this because..."
Verified Factor Detective
