This prime factorization worksheet lets 5th graders complete five factor trees and write each number's prime factorization. A full answer key is included, making it perfect for no-prep practice, homework, or math centers.
A Florida FAST 4th grade math practice test workbook for teachers, with a pretest, skill practice for all 39 benchmarks, mixed review and 2 full-length practice tests. Answer key included, so test prep is ready to go.
This Prime Numbers Worksheet helps 4th graders identify prime and composite numbers by listing every factor and explaining their reasoning in a word problem. An answer key is included, so practice is fast to assign and easy to check.
A Smarter Balanced (CAASPP / SBAC) 4th grade math practice test workbook for teachers, with a pretest, skill practice for all 38 standards, mixed review and 2 full-length practice tests. Answer key included, so test prep is ready to go.
A NJSLA-A 4th grade math practice test workbook for teachers, with a pretest, skill practice for all 30 standards, mixed review and 2 full-length practice tests. Answer key included, so test prep is ready to go.
Using this 4.OA.4 Fourth Grade Common Core lesson students determine whether a given whole number in the range 1–100 is prime or composite.
This planet prime vs planet composite activity is a number-card sorting game for 4th and 5th grade, with a recording sheet and factor pair practice page. Answer key included for quick checking.
Numbers that refuse to be split
A prime number has exactly two factors: 1 and itself. So 7 = 1 × 7 is prime, but 12 = 3 × 4 is composite because it has more factors. Students usually meet primes in 4th grade, finding factor pairs and sorting numbers up to 100 into prime and composite. Later they use prime factorization to break numbers into prime building blocks, like 12 = 2 × 2 × 3. The click comes when kids realize 1 isn't prime at all, and 2 is the only even prime!
Primes make sense when kids can see factors, not just memorize a list. Here's what works for us.
Give kids 12 square tiles and ask how many different rectangles they can build. Then try 7. Seven only makes one long row! Numbers that make just one rectangle are prime, and kids discover it with their own hands.
Why it works: kids understand an idea best when they touch it, then draw it, then write it, the order the U.S. Department of Education recommends for elementary math.
Try it withPrime Numbers WorksheetWorksheetsOpen it →Write a number on the board and have partners decide prime or composite, then convince the class with a factor pair. Pick sneaky ones like 51 or 91 so they have to check carefully.
Why it works: using clear, consistent math words out loud is one of the U.S. Department of Education's recommendations for elementary math.
Try it withPrime Factorization WorksheetWorksheetsOpen it →A short song gets the first few primes into kids' heads fast. Play it as a warm-up all week, then pause it and have the class shout the next prime.
Why it works: words set to a repeating melody are easier to recall than the same words spoken (Wallace, 1994).
Try it withPrime Numbers SongSongsOpen it →Primes are a natural fit for puzzles and games.
ActivitiesKids sort number aliens onto the right planet by checking their factors.
Open Planet Prime vs Planet Composite Activity →
Test PrepOn a 100 chart, cross out multiples of 2, 3, 5 and 7. Every number left standing (except 1) is prime!
Open Florida FAST 4th Grade Math Practice Test Workbook →
Test PrepPartners race to build factor trees for the same number and see if they end with the same primes.
Open Smarter Balanced (CAASPP / SBAC) 4th Grade Math Practice Test Workbook →Teacher favorites right now: Prime Factorization Worksheet, Florida FAST 4th Grade Math Practice Test Workbook and Prime Numbers Worksheet.
A prime number is a whole number greater than 1 that can only be divided evenly by 1 and itself. Examples are 2, 3, 5, 7, 11 and 13.
No. A prime must have exactly two factors, and 1 has only one factor, itself. So 1 is neither prime nor composite.
Most students learn prime and composite numbers in 4th grade, working with numbers up to 100. Prime factorization usually follows in 5th or 6th grade.
Have them try dividing by small primes: 2, 3, 5 and 7. If none of those divides evenly into a number under 100, it's prime. Even numbers bigger than 2 are never prime.
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