In this study, it was aimed to investigate the perceptions and competences of prospective science teachers about formative assessment approaches. Qualitative case study methodology was used in the study. Research group consisted of 17 senior students of science education. As a data collection tool, a semi-structured "Formative Assessment Perception Interview Form" was used which was developed by the researcher. The data were collected by conducting a total of ten in-depth interviews, 8 with focus groups and another 2 as face -to-face. Collected data were subjected to content analysis. Study findings revealed that perceptions and competences of prospective science teachers on formative assessment approaches are very low and not sufficient. In particular, it was found out in this study that prospective science teachers are familiar with the definition and function of formative assessment approaches (12%) at a low extent albeit; however, they are seriously deficient about for what purpose (7% competence) they will use and choose them, how to prepare such approaches (3% competence), how to interpret and score effects of the results for the learning-teaching process (2% competence). Science teacher training curricula need to be revised in a way to give prospective teachers a training and preparation in practical, long-term and real learning-teaching environments for formative assessment approaches.