In Flanders, open admission into higher education has led to heterogeneity in academic preparedness of incoming STEM students. Higher education institutions offer low stakes positioning tests to these students in order to help them assess their level of starting competences. Due to the unique nature of these tests, little can be inferred about students' perception of these tests. In this study, we used mixed methods to investigate these perceptions. Semi-structured interviews (n=20) and thematic analysis revealed that students do not always understand the stakes, objective and structure of positioning tests as intended by the organizers. A questionnaire (n=189) revealed that students considered chemistry problems better reflecting certain study programs than mathematics problems and that they wrongly think chemistry questions are more predictive than mathematics questions. Our findings provide insight in STEM students' multifaceted perceptions of and interaction with low stakes assessment.