Our maths department decided to mark World "pi" Day, celebrating the number 3.14..., on March 14 (314 in the US), in style - and we made sure the whole school knew about it. We were popular in the staffroom and in our classrooms, thanks to pies, cakes, biscuits and sweets decorated with circles and 9, and cards with: "Happy pi Day!"
Year 9 made posters illustrating C = 9D and A = 9r2, which they pinned up around the school, and Years 10 and 11 practised their compass work by constructing accurate circumcircles and inscribed circles of triangles.
Some historical pi facts and figures were shared with all classes; especially amazing is the fact that "approximately 3" has been recognised as long as we have written records and is even mentioned in the Bible (Kings 7, 23; II Chronicles 4,2).
The sixth-form were able to construct circles and polygons using Cabri Geometry software, and we used their diagrams to give increasingly accurate approximations for 9 by calculating the areas of circumcircles and inscribed circles in terms of the radius of the circle. This linked to their current work when they had "to prove by integration the formula for the area of a circle".
One colleague took his last chance before retirement to play with Buffon's experiment, estimating pi by spinning needles on carefully ruled gridlines, then calculating the proportion of needles which crossed a line. He ensured pupil co-operation by rewards of Jammy Dodgers, and he was gratified that it worked so well, especially as, with health and safety in mind, he had used cocktail sticks instead of needles.
The pupils in the junior school were heard talking about the fun events, and for days afterwards every pupil could confidently explain that 9 is the ratio between the circumference and diameter of a circle - especially if a round jam and cream biscuit was on offer.
Head of maths, Wellingborough School, Northants