The prime team

Students will learn their prime numbers by creating and manipulating their own Sieve of Eratosthenes.

A lesson plan for grade 6 Mathematics

By Lori Bradley

Learn more

Related pages

• Math Fun: We have compiled some of our favorite mathematics instructional resources to help students develop a sense of numbers and how they are used by us everyday. Students will have fun practicing their skills and trying new problem-solving ideas.
• Adding fractions with unlike denominators/The numbers tell LCD: Students will be able to find the Lowest Common Denominator by using prime factors. They will then add the fractions. This method was developed for students who have problems guessing and checking.
• In math, "elegant" means "cool"!: An elegant solution to a math problem is one that requires less time and work. Encouraging students to find such solutions will help them build number sense or numeracy.

Related topics

• Learn more about composite numbers, mathematics, prime factorization, and prime numbers.

Help

Please read our disclaimer for lesson plans.

Legal

Learning outcomes

Students will work with a partner to manipulate numbers and identify prime numbers less than 100.

Teacher planning

Time required for lesson

90 minutes

Materials/resources

• Teacher made counters 1-100
• Construction paper
• glue

Pre-activities

Review rules for divisibility - take notes. Introduce the activity and discuss criteria for success: identify prime numbers less than 100; neatness and completeness of finished Sieve.

Activities

1. Teacher divides the class into teams of 2 or 3 students. Provide each team with paper counters 2 - 50. Fold/divide the construction paper in thirds. Students should label the first column “neither”, the second column “prime”, the third is labeled “composite”.
2. Have students place 1 beneath the “neither” label. I use the analogy of a team. The “1″ is the coach and plays on neither team.
3. Have students remove counters that meet the rules for divisibility:
   • Remove all counters that end in 0, 2, 4, 6, 8
   • Remove all numbers that end in 0 or 5.
   • Remove all numbers whose sum is divisible by 3, for example, 21: 2 + 1 = 3.
   • Remove all numbers that can be divided by 4.
   • Remind students to use their 4 math facts.
   • Remove all numbers whose sum is divisible by 9, for example, 27: 2 + 7 = 9.
   • Remove all numbers that end in double digits, for example, 22, 33, 44. (except 11)
4. Teacher should monitor and guide students. When all students have removed their composite numbers, tell them that the remaining numbers are Prime. If done correctly, this process will identify all the prime numbers.
5. Have students place their prime numbers beneath the “prime” label. Visually assess for understanding. Have students write or tell the rule for prime numbers (only 1 x that number will give the “answer”.) At this point if the students are not able to use correct terminology ie. product and factor they will still have a working knowledge of primes.)
6. All remaining numbers are placed beneath the “composite” label. Ensure that 11 goes in the prime column.
7. Have students glue their numbers on the construction paper in the proper location.
8. For independent practice, have students complete a Sieve for numbers 50 - 100 using the same steps.

Assessment

Visually assess understanding by checking for completeness of both group and independent practice.

Supplemental information

Comments

I have used the traditional Sieve — marking out the composite numbers — but found that many of the students just randomly crossed out numbers in order to “finish” the assignment. This method is more hands on and allows the teacher time to monitor and guide progress.