The purpose of this lesson is for students to explain why it is possible to find a common denominator of two given fractions by multiplying the denominators. 

In this lesson, students begin to develop formal strategies for adding and subtracting fractions. They deal with all cases, including situations in which the two denominators share no common factor and situations in which the denominators share a large factor. Students show why the product of the two denominators is always a common denominator but are encouraged to use the common denominator that makes sense to them. The discussions focus on different choices students make for a common denominator, how their calculations are the same, and how they are different.

Reflect on a time your thinking changed about something in class recently. How will you alter your teaching practice to incorporate your new understanding?