This Instructional Activity is a part of the Lesson 25, Unit 4, Grade 6. Students learn the definition of solution in the context of placing a value into a variable to see if that value makes the equation true. In previous lessons, students used sentences and symbols to describe the values that, when substituted for the variable in an equation, resulted in a true number sentence. In this lesson, students make the transition from their previous learning (e.g., substituting numbers into equations, writing complete sentences to describe when an equation results in a true number sentence, and using symbols to reduce the wordiness of a description) to today's lesson where they identify the value that makes an equation true as a solution.