Common Core Math 4.OA.4: May be used separately or with my Smartboard lesson, which outlines the step-by-step method to eliminate composite numbers from the hundreds chart, leaving only prime numbers. Using activity sheets in the lesson, students will determine the prime numbers between 1 - 100. The Sieve of Eratosthenes is a quick and easy method for finding primes and composite numbers under 100. Prior knowledge of factors and multiples is needed. The activity reinforces the concepts of factors, multiples, and composites, as well as assisting students to understand why specific numbers are either prime or composite. Prerequisite learning for converting fractions, multi-digit division, and algebra.