Lesson Plan

Prime and Composite Numbers

Take your understanding of factors one step further! Use this lesson to classify factors as prime and composite numbers while creating factor trees.
Need extra help for EL students? Try the Conversations About Prime and Composite Numbers pre-lesson.
View aligned standards
Need extra help for EL students? Try the Conversations About Prime and Composite Numbers pre-lesson.

Learning Objectives

Students will be able to find factor pairs for whole numbers and determine if they’re prime or composite numbers.

The adjustment to the whole group lesson is a modification to differentiate for children who are English learners.
EL adjustments


(10 minutes)
Factor RainbowsFactor Tree
  • Display the teaching component at the top of the Factor Rainbows worksheet. Ask students to turn and talk to their partners about how to complete the rainbow. Listen for key terms such as "factors" and "math expressions."
  • Choose a student to share their answers and allow other students to add to their answers or offer corrections.
  • Define factors as numbers we can multiply together to get another number and show how the rainbow has factors that, when multiplied, produce the whole number on the rainbow.
  • Explain that today they'll expand their understanding of factors by determining if the factors are prime numbers or composite numbers.
  • Define prime numbers as whole numbers that can only be made by multiplying the number one by itself. Tell them if they cannot divide a number by any other number than itself and one, it is prime. Define composite numbers as whole numbers that have factors in addition to 1 and itself. Tell students 1 and 0 are neither prime nor composite.
  • Ask students to shout out which numbers they think are prime and write them on the board in a T-chart with "prime" and "composite" written on top. Correct any misconceptions with multiplication sentences and/or visuals, or allow other students to offer explanations.


  • Place students with a sympathetic partner who can explain rainbow factorization well.
  • Give a student-friendly definition in students' home language (L1) and English (L2) for new vocabulary as you come across each term.


  • Allow time for students to consult with a partner before they shout out examples of prime and composite numbers.