Beacon Lesson Plan Library

Prime Factorization Mobile

Amelia McCurdy
Santa Rosa District Schools


During this review lesson, students demonstrate their knowledge of prime numbers, composite numbers, and prime factorization using exponents to create a factor tree mobile.


The student knows word names and standard numerals for integers, fractions, decimals, ratios, numbers expressed as percents, numbers with exponents, numbers expressed in scientific notation, and numbers expressed using the square root radical.

The student knows if numbers are prime or composite.

The student determines the prime factorization of a composite number.


-3 x 5 Index cards (unlined)
-Yarn (cut into 6 to 8 inch lengths)
-Colored Pencils, markers, or crayons
-Hole puncher
-Ceiling Hooks (large paper clips or commercial)


1. Prepare a mobile as an example
2. Create sets of prime and composite numbers to assign to students


1. Review prime numbers, composite numbers, and prime factorization. Ask students to give you examples of prime and composite numbers. Review how to find the prime factorization using a factor tree and how to write the prime factorization using exponents. Provide opportunity for practice.

2. Describe the project. Assign two numbers to each student, one prime and one composite. After the students determine which numbers are prime and which are composite, they will plan their mobile by drawing a factor tree for the composite number. Encourage students to find several ways to create a factor tree and select one. Students are required to rewrite their number in prime factorization using exponents. Each number on their factor tree is one index card. On the back of their number card, the students will write the number in exponential form. Each line (tree branch) is a piece of yarn. Students need to determine how many cards and pieces of yarn are needed for their mobiles. See attached file for an example mobile.

3. Students will bring their plans to the teacher for approval and tell the teacher how many cards and pieces of yarn are needed for their project. Encourage students to be creative in their designs. For example, write the numbers in 3-D form.

4. After the projects are completed and graded, hang the mobiles for display in class.


Scoring Rubric of project:
- Whole number correctly rewritten
3 points--correct and using exponents
2 points--correct and without exponents
0 points--incorrect
- Identify prime number
3 points--correctly identifies prime number
2 points--correctly identifies with help
0 points--incorrect

- Identify composite number
3 points--correctly identifies composite number
2points--correctly identifies with help
0 points--incorrect
- Design mobile
3 points--correct
2 points--correct with help
0 points--incorrect
Students who do not score at least 8 points will need additional instruction and practice.


For lower level students, have students work in cooperative groups. For advanced students, students could create a mobile for numbers greater than 100. For Pre-Algebra students, use positive and negative integers. For Algebra students, create a mobile for monomials.
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