The purpose of this study was to explore prospective science teachers' pedagogical reasoning skills by analyzing what they look for in middle school student's written exam responses, how they evaluate these responses, and how they plan to use these responses. The study was conducted as a case study. Seventy-six prospective science teachers who have taken the assessment and evaluation course participated in the study. The data was collected using a form that contained the responses of middle school students to the two open-ended questions on color formation and light. It was analyzed through the content analysis method. According to the findings, prospective teachers evaluated examined the student responses superficially, prioritized whether the responses were correct or incorrect, over-diagnosing the subject matters students had problems with, did not provide evidence for the claims they put forward while evaluating, and developed evaluations on students' conceptual learning without establishing a connection among a student's responses to different questions. These results reveal the significance of having practical training on how to evaluate and use student responses as part of prospective teachers' training on assessment and evaluation and that, through this training, they can develop their pedagogical reasoning skills.