This math lesson teaches students how to use the Angle-Angle or the Equal Side Ratio theorem to determine if two triangles are similarity. The lesson includes research-based strategies and strategic questions that prepare students for standardized assessments. In this lesson, students will identify known information and determine which theorem applies, then use the theorem to prove the triangles' similarity. In addition to the lesson, there are two pages of independent practice and three pages of periodic review with questions modeled after standardized assessments.