4th grade prime & composite numbers worksheets

Prime and composite worksheets ask fourth graders to classify numbers from 2 to 99 by counting their factors. Primes have exactly two factors; composites have more. Deciding takes a quick divisibility check with 2, 3, 5, and 7.

Free printable PDF worksheet, aligned to Common Core 4.OA.B.4.

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The kind of problems you'll get

Write prime or composite.

  1. Is 83 prime or composite?

    Answer: prime

  2. Is 9 prime or composite?
  3. Is 17 prime or composite?

Every print pulls a fresh set of problems at this level, so a make-up test or a second sibling never gets the same sheet.

What's on each sheet

Every version prints on US Letter or A4, with its answer key on the last page.

How to teach this

Give your child a short test sequence instead of guessing: is it even? Do the digits add to a multiple of 3? Does it end in 5 or 0? Then try 7. Any yes means composite; all no's on a number under 100 means prime. Keep the trap numbers coming back: 51, 57, 87, and 91 catch almost everyone once.

Watch for: Kids call every odd number prime, but 9, 15, 21, and 51 are all odd and all composite, so odd only means 'not divisible by 2'. Kids label 1 as prime. It has only one factor, so it is neither prime nor composite.

Common questions about prime & composite numbers

Why isn't 1 a prime number?
A prime needs exactly two different factors, and 1 has only itself. Mathematicians count it as neither prime nor composite.
How can my child check a bigger number like 91 without a calculator?
Try the small primes in order: 2, 3, 5, then 7. For 91, the first three fail but 7 × 13 = 91, so it's composite, and for any number under 100, checking up to 7 is enough.

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Aligned to Common Core 4.OA.B.4. Reviewed by the One more sheet curriculum team. Content version 123, updated July 2026.