This paper focuses specifically on the reasoning skill called proportional reasoning. Areas addressed include: (1) a definition (providing examples of direct and indirect proportional reasoning); (2) the development of proportional reasoning (discussing survey results of students logical reasoning abilities); (3) planning for the future (proposing steps for increasing students' understanding of proportional reasoning and analyzing the teaching approaches used in other countries where the development of proportional reasoning has been more successful and convey this information to U.S. teacher training institutions); and (4) a mental processing model for proportional reasoning (presenting a model which identifies a hierarchy of skills and mental processes needed for proportional reasoning). A list of 18 references is included. (ML)