I use this activity to bridge the gap between an algebraic proof to a geometric proof.
Generally, I model the steps to solving an Algebra 1 multi-step equation (i.e. 5x + 6 = 8x -12). Then I describe the properties of equality that allow me to progress through the problem to an answer. Then I rewrite the progression of the problem into a 2-column proof. Its an easy conversion.
Provided is a form that gives space to solve three Algebra 1 problems with three blank 2-column proof forms. The students can then work in groups and share out there final 2-column proofs. The file is a Microsoft Excel Spreadsheet.