March 14 is 3-14, the first three digits of the mathematical constant Pi. This makes it a perfect day to practice math with kids and explain the importance of this number for measuring the various aspects of a circle. Pi is the ratio of a circle's circumference divided by the diameter. The sequence has been calculated to trillions of digits and people have set records memorizing thousands of digits for various contests.
For Pi day activities include eating pie, measuring the distance around the pie's edges and comparing that to the diameter, and determining the area of the pie. Area = π(r squared). Because Pi is a constant this ratio remains the same no matter what size circle you are measuring from a quarter to a pizza, or even the Earth.
More information about Pi day can be found at Pi Day.org. The Pi symbol can be found on just about anything and finding desserts shaped like a circle can be a lot of fun for kids. Pay special attention to 1:59pm, which is 3.14159. This is a very unique opportunity to teach kids about math in a fun fashion.