Pi Day may seem like a Mathematical holiday that is just for upper level Math classes but here are a couple of ideas to use in Elementary!
Upper Elementary: Students can view this explanation of Pi from this website. http://wonderopolis.org/wonder/what-is-pi Then they can create a paper plate representation similar to the picture I have included. Have the students to measure the circumference, radius, and diameter of the paper plate and then put their division skills to the test as they divide the circumference by the diameter to see if they get 3.14 (Pi).
Lower Elementary: Students can view the decimal representation of Pi. Then they can use manipulatives, beads, or any other material the teacher has available to practice recognizing numbers and odd and even numbers. If they create bracelets with beads and pipe cleaners then they can wear their creation on pi day!
Of course it is always a good idea to actually celebrate Pi Day by eating PIE!!! Have fun learning!