We investigated how pre-service teachers (PSTs) interpret their calculations in proportional tasks. A written questionnaire was administrated to 199 PSTs and an inductive content analysis approach used for data analysis. We found that one item that asked PSTs to interpret the meaning of their results had unusually low success; open coding on the responses revealed several common themes. We argue these common errors cannot be dismissed as simple unit or rounding mistakes; they are a reflection on how respondents think about quantities, story problems, and the nature of mathematics itself. We end with suggestions on how to address this problem. [For the complete proceedings, see ED606531.]