Properties of Diagonals

This lesson comes straight up stolen from @pamjwilson. I used it last year for the first time as a full class period lesson. I used it again this year as an intro into properties of quadrilaterals.

She explains it way better than me so you can go read it. Seriously. Go. But I can share some photos from my class and the INB pages we did last year.

This is based off of an activity called The Kite Task but I couldn't find any more information on it other than what Pam posted about.

Here's the literal kite shape. The green and blue 'braces' are two different lengths. Each student gets a combination of three pieces so that they can build with congruent diagonals and without. A gold brad or fastener is used to hold them together and then they trace. Last year we used legal sized pink paper and this year they literally drew on the desk (with dry erase markers).

Next year I'm thinking chart paper and making them go to the board and switch writers each time so that there is more participation. Maybe even a competition to see which group can get the most unique combinations?

Not going to lie, the students struggled with creating different combinations besides the one example of the kite that I showed them to start with. I had a few students who I think had no idea what had just happened at the end of the activity.

A lot of students started by literally tracing the braces so we had to go over the fact that we were looking for four-sided figures.

Last year we did an entire set of INB pages just on diagonals. This year I incorporated it with our quadrilateral properties pages. Here are pictures of both.

What other suggestions do you have to make this activity better?


  1. I'm always curious when I have a spike in visitors...thanks for shout/out! I love so many things about this lesson. It is a bit of struggle for some to consider the braces...are not the sides of the quadrilateral. Love the updates with INB, etc. Should I ever get to teach geometry, I will definitely use your suggestions!

    1. I feel like there's a simple thing missing that will make all the difference...I'm just not sure what it is!