Sir Cumference and the Dragon of Pi

In this entry in Cindy Neuschwander''s Sir Cumference series, Sir Cumference has drunk a potion that turns him into a dragon, and his son Radius has to work out the antidote — a measurement hidden in the relationship between a circle''s circumference and its diameter. The plot is a vehicle for one idea, delivered properly: that every circle, whatever its size, has a circumference a little more than three times its diameter, and that this constant is what we call pi. Wayne Geehan''s illustrations carry a good deal of the mathematical weight, showing the measurements being made rather than just decorating the page.

Homeschool families tend to use it in one of two ways. The most common is as the opening of a hands-on lesson: read the story, then hand the child a piece of string and a collection of round objects — a can, a plate, a bicycle wheel — and have them measure circumference and diameter and divide. Discovering 3.14 for themselves, in their own slightly imprecise numbers, is the point, and the book sets that up better than a textbook page does. The second use is simply as a Pi Day read-aloud, where it does the job without much preparation.

Be clear about what it is and is not. This is a thirty-two page picture book, not a curriculum, and it teaches one concept. Reviews from parents are consistent on that: excellent for introducing or cementing pi, not a substitute for instruction on area or on working with the formula. The wordplay that runs through the series — Radius, Sir Cumference, the Circumnavigators — delights some children and sails past others, and a few parents find the puns heavy going on a third reading. Best suited to roughly second through fifth grade, and it works well alongside the other titles in the series if a child takes to them.