Proportional reasoning is important to the field of mathematics education because it lies at the crossroads of additive reasoning in the elementary school and multiplicative reasoning needed for more advanced mathematics. This research reports on the representations used by pre-service teachers (PSTs) as they responded to tasks involving proportional reasoning. The findings highlight three common difficulties that were prevalent among participants' responses. An analysis of the representations used by participants revealed that the representations that PSTs created in their effort to solve the problems often enabled them to overcome these difficulties. Prior research is used to hypothesize explanations of the extent to which different forms of representations were useful and productive for the participants. Implications include ways that use of these multiple representations could aid in the teaching of proportional reasoning. [For complete proceedings, see ED581294.]