One of the standards on the CCRS dealing with reasoning with equations and inequalities is:

Explain each step in solving a simple equation as following from the equality of numbers asserted at the previous step, starting from the assumption that the original equation has a solution. Construct a viable
argument to justify a solution method.

Students will have to be able to explain steps in solving simple linear equations. They will also have to construct viable arguments to justify solution methods. A really great way to have students develop and practice this ability is through writing. The url link above will take you to a Math Memo written by Tyler Holzer with a ready-to-use activity for your students, as well as samples of work from when he did it with his lesson.