Factor rainbows: a 20-minute 4th grade factors activity
What it is: a 4th grade math activity where students list all the factors of a number in order and connect each factor pair with a colored arc, making a "rainbow." The rainbow shows when they have found every pair and makes square numbers and primes easy to spot.
Time: about 20 minutes. Grade: 4th grade.
Materials: paper, colored pencils, and a list of numbers to try (12, 16, 18, 24, 29, 36, 48).
- Model 12: write 1 and 12 at the ends, then 2 and 6, then 3 and 4. Connect each pair with an arc in a new color.
- Ask: "How do we know we found them all?" Point out that the arcs meet in the middle.
- Students make rainbows for 4 or 5 numbers from the list.
- Look at 16 and 36: one factor has no partner. Ask: "What is special about these numbers?"
- Look at 29: it has only one arc. Name prime and composite numbers and sort the list.
Differentiation: students who need support use a multiplication chart while they search. Students who are ready find a number under 100 with the most factors. English learners can use the frame "The factors of ___ are ___."
Quick check: ask a student to make a factor rainbow for 20 and say whether it is prime or composite.
For more ideas at this grade, browse the other free activities on the Hub.
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About this resource
- Shared by
- @UpOnlyLearning · Curriculum team
- Posted
- Oct 30, 2026
- Type
- Lesson plan
- Grade
- Grades 3–5
- Subject
- Math
- Language
- English
- License
- Free for classroom, co-op and tutoring use. Please don't resell.