*This post originally appeared on the blog Education With Doc Running. *

Pi Day is on its way! And who doesn’t love a little pi (and pie)? On Pi Day (3.14), we celebrate Pi, that wonderful irrational number that we first discover when we are studying circles and is used over and over again in geometry, trigonometry, and beyond.

One of my students’ favorite activities for Pi Day is to use inquiry to literally find Pi and its relationship to the circumference of a circle. Even though some students already can tell you the formula for circumference, few have actually proved it. Not only do we have a great Pi Day activity, but also students practice that important skill of developing proofs which they will see more formally in upper level mathematics classes. This is a great activity for upper elementary and middle school students.

### Here’s what to do:

- Set up several cylindrical objects for small groups of students – cups, plates, clocks, pie pans, biscuit or cookie cutters, etc. (I ask students to bring in cylinders that are not breakable so that we have even more choices.)
- Give each group several pieces of string that are longer than the circumference of the cylinders. Depending on the size of the cylinders 18″ strings should be sufficient for most cylinders. (NOTE: string is better than yarn, because yarn can stretch and distort measurements.)Set up several cylindrical objects for small groups of students – cups, plates, clocks, pie pans, biscuit or cookie cutters, etc. (I ask students to bring in cylinders that are not breakable so that we have even more choices.) Give each group several pieces of string that are longer than the circumference of the cylinders. Depending on the size of the cylinders 18″ strings should be sufficient for most cylinders. (NOTE: string is better than yarn, because yarn can stretch and distort measurements.)
- Have students measure the distance around and across 4-5 objects with the string.
- Students record their findings.
- Students then analyze the relationship between the diameter and the circumference. It can help to think of the relationship as how many distances across does it take to make the distance around. Students will discover that the ratio (ooh, look another math concept just tossed in there) is around 3.14 (or 22/7) for all the circles.

One of my favorite parts of this activity is that it is more meaningful for students than simply memorizing the circumference or the value of pi.

For elementary school students, you can close out the activity by reading Sir Cumference and Pi aloud or just sharing the Sir Cumference book series for students to read on their own. When we do this activity on Pi Day, we all eat pie (usually hand pies which are easier in class). You can find a complete activity guide with student pages here or just create it on your own. You can find more Pi Day activities here.

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Education with DocRunning is a secondary teacher in California. She holds a Master’s in Education and a PhD in Education Policy. In addition to teaching in a gifted program, she also owns her own education policy research firm and is working on her first book. Her classroom and research experience have shaped the student-centered philosophy she takes in developing curriculum. She blogs at Education With Doc Running about teaching as well as what’s going on in the education world. And of course, she runs daily.