What is proportional reasoning, anyway?

There appears to be a correlation between some measures of scientific reasoning skills and gain on conceptual measures of student understanding of introductory physics such as the Force Concept Inventory. At NMSU, we have established a correlation between pretest scores on proportional reasoning tasks and student performance on conceptual post-tests in the introductory lab. Proponents of a Piagetian model of cognitive development would call these scientific reasoning skills `operational capacities'' that signal the last transition in human intellectual growth from ``Concrete Operational'' to ``Formal'' reasoning. Seen in this light, the correlations described above suggest a cognitive ``deficit'' associated with development. We are exploring the possibility that proportional reasoning may in fact be a blanket term to describe many smaller elements of skills which students often seem to lack. In this talk, I will present some initial results from our investigation.