A 12-episode constructivist teaching experiment with two pairs of elementary preservice teachers was conducted to examine how they reason distributively and proportionally. Specifically, I studied how prospective teachers reason with ratios as multiplicative comparisons. Prospective teachers solved different problems in one specific context (Step Problems) that require to reason with ratios as multiplicative comparisons, and represented their pictures during the episodes and the follow-up interviews. Second-order models of four prospective teachers were made. In this study I found that reasoning with ratios as multiplicative comparisons in that specific context of problems was challenging for prospective teachers and all four had considerable difficulty. Only one of the four prospective teachers fully reasoned with ratios as multiplicative comparisons. The findings of this study provide teacher educators with a new perspective on prospective teachers' quantitative understanding of proportional reasoning, a domain as we know little about, and has implications for the mathematical preparation of prospective elementary teachers.