Theories of mathematics problem solving (25,33,50) have placed a major focus on the
role of heuristics. Surely it seems that providing explicit instruction on the development
and use of heuristics should enhance problem solving performance; yet it is not that
simple. Schoenfeld (35) and Lesh (19) have pointed out the limitations of such a
simplistic analysis. Theories must be enlarged to incorporate classroom contexts, past
knowledge and experience, and beliefs. What Polya (26) describes in How to Solve It is
far more complex than any theories we have developed so far.