In this study we explored to what extent middle school teachers were able to appropriately identify proportional situations when presented with various mathematical structures and if there were relationships between attributes of the teachers and their ability to identify proportional situations. Interestingly, there were no strong relationships aside from teachers' perception of their knowledge of mathematics and their ability to identify proportional situations. Teachers were also found to correctly identify proportional situations significantly more often than non-proportional situations. Nearly one third of the teachers misidentified non-proportional linear situations as proportional. Thirteen participants' responses to such a situation were analyzed qualitatively resulting in some common knowledge resources that they appeared to use when attempting to identify whether a situation was proportional or not. [For the complete proceedings, see ED583608.]