This study investigates the knowledge acquisition of biology and physics freshmen students with special regard to differences between high school (HS) high performing and low performing students. Our study is based on a prior knowledge model, which describes explicit knowledge as a composite of four knowledge types: knowledge of facts, knowledge of meaning, integration of knowledge, and application of knowledge. As a first outcome-oriented approach, we operationalize knowledge acquisition via the changes in these knowledge types between the beginning and the end of the first year. To investigate the knowledge acquisition, a test set was constructed that covers these knowledge types. It was administered to 162 biology and 101 physics students at university. We used an Item Response Theory approach to scale the data. Repeated measures ANOVAs were used to analyze the acquisition of the knowledge types. We separated HS low, medium, and high achievers by high school grade point average (HS GPA). The knowledge acquisition of the HS low achievers did not differ from other groups. However, the HS low achievers did not only start with less prior knowledge but also were not able to reach the prior knowledge of the HS high achievers within the first year. Our findings concerning knowledge acquisition may be used to support and improve students' knowledge acquisition in a targeted way by focusing on selected knowledge types.