I suspect that one of the reasons why people are drawn to pie charts is the fact that these charts are familiar from elementary school instruction in the meaning and mathematical use of fractions. Based on this instruction, a pie chart is the image that becomes strongly associated with the parts-of-a-whole concept (a.k.a., fractions). But, just because this is how fractions have been traditionally taught in schools, should we assume that pie charts are the best visual representation for learning fractions? Although the metaphor is easy to grasp (the slices add up to an entire pie), we know that visual perception does a poor job of comparing the sizes of slices, which is essential for learning to compare fractions. Learning that one-fifth is larger than one-sixth, which is counter-intuitive in the beginning, becomes further complicated when the individual slices of two pies—one divided into five slices and other into six—look roughly the same. Might it makes more sense to use two lines divided into sections instead, which are quite easy to compare when placed near one another?
This not only makes sense based on our understanding of visual perception, but recent research has demonstrated that it in fact works better for learning. Take a moment to read the recent article about this by Sue Shellenbarger in The Wall Street Journal entitled “New Approaches to Teaching Fractions” (September 24, 2013).