Prime Factorization Lessons for Kids
- Begin the lesson by explaining to students the difference between prime numbers and composite numbers. Ask students to cut 55 small squares out of construction paper. The students then write the prime numbers between 1 and 20 individually on each square. Each student should have five squares for each number and 10 squares with multiplications signs. Write a number on the blackboard so that the entire class can see it. Ask students to use their squares to create the number. For example, if the number on the board is 30, the prime factorization is 2 x 15.
- Pass out grid paper to each student. Ask the students to define factorization. Then ask them to factor out a variety of numbers by drawing rectangles on the grid. Each square in the grid is a factor. At this point, they can use both composite and prime numbers to factor the larger number. Explain to the class the difference between prime numbers and composite numbers. Now have students draw rectangles using only prime numbers to factor out the same numbers as before. See how the rectangles change dimensions.
- Teach students how to draw factor trees. Start at the top of the tree with a large, even number at least five digits long. Draw two lines down from the first number for the first two branches. Place the first two factors of the large number at the bottom of each branch. Draw two lines down from these two numbers. Add the two factors whose product is that number. Continue adding branches until the last row is only prime numbers. Finally, have students multiply the bottom level to find the top number to demonstrate prime factorization.
- Show prime factorization with the upside-down division method. Start with an even number at least three digits long. Draw a line in front of the left-most digit of that number. Now draw a line that creates an "L" with the first line. The bottom of the "L" goes under the number. Place a 2 to the left of the "L." Divide the number by two, placing the product under the bottom line. Continue downward by dividing the product by 2 and then the product of that number by 2 until the end product is a prime number.
