Tuesday, October 4, 2016

How a hole puncher saved the day: Proving Lines Parallel Proof Activity

Even in the 7th week of school, Geometry proofs still strike fear into my little freshmen. For today's lesson on proving lines parallel, I knew I wanted them to do proofs. I found this great cut and paste activity from Amazing Mathematics. I chose to print the version that has the statements filled in and students only have to come up with the reasons for each step. By the time we get to triangle congruence, they will be writing both sides, but I was OK with giving them the outline today.

We reviewed all the theorems and converses and theorems and did a few examples together in their interactive notebooks, and then I set them lose on the proofs. I have my students grouped in threes, which is plenty of brain power to figure out these proofs. I gave each group a strip of paper and had them write the numbers 1-6 on it. Each group started with a proof (I only used 1-4 in the first round because they get increasingly more difficult). They worked together to correctly place the reasons in the proof. When the group agreed, they called me over for a check.

If it was right, I took my blue marker and scribbled off the number of the proof they finished. Then I saw a student look the other blue markers in my supply box with a gleam in his eye. And I realized with this system, there is no way I would be able to keep them from cheating. I changed the scribble to my initials, and then I had a better idea... I dug into the depths of my desk drawer and I got out my single hole puncher and punched a hole over the number when they completed it. The students LOVED it! It's amazing how something so simple totally changes the game. Then they wanted to use the hole puncher - and they would fight over whose turn it was to make the punch. The click of the puncher and the creation of the hole was as satisfying as correctly completing the proof. After I (or they) punched the number, they scrambled up the pieces and took it to the middle table and exchanged it for another proof. They kept doing this until they finished all six proofs.

Typically telling students they would be completing six Geometry proofs to prove lines parallel would be met with moans and groans, but my students were very engaged and motivated to finish the problems. I definitely see my hole puncher making future appearances in class!

Next they are going to try out this Proving Lines Parallel Crossword Puzzle. The outline of the proof is still there, but they have to come up with some missing statements and reasons. They still get the self-checking benefit of the crossword puzzle though.


  1. I LOVE LOVE LOVE this idea. Isn't it hilarious how something as simple as a hole puncher rocks their world? LOL

    1. I know! Imagine if I would have had one of those fun hole punchers that make a shape!


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