Decision-making in socioscientific issues (SSI) constitutes a real challenge for both biology teachers and learners. The assessment of students' performances in SSIs constitutes a problem, especially for biology teachers. The study at hand was conducted in Germany and uses a qualitative approach following the research procedures of grounded theory to focus on teachers' concepts and, especially, coping strategies in assessment concerning students' decision-making in SSIs. Semi-structured interviews with six teachers, in combination with video-vignettes, were used for data generation. The results show predominantly defensive strategies when teachers are confronted with the assessment of students' performances in SSIs. These results and implications for teacher education and teacher training are discussed.