BACKGROUND: Students frequently explain evolutionary processes, such as adaptation, in a teleological way. These teleological explanations may involve goal-directedness, purpose, an external designer or the internal needs of individual organisms as causal factors. While many science educators consider teleological bias to be a central obstacle in understanding evolutionary processes, other scholars argue that teleological (and anthropomorphic) formulations may also serve pedagogical aims, e.g., to increase empathy and to relate topics to students’ world. Although many empirical studies describe the abundance of students’ teleological explanations, little is known about how teachers deal with teleological explanations in the classroom and the relationship between teachers’ approach and students’ learning processes. Consequently, this study addresses the research question of how a teacher and students situationally address teleology across a teaching unit on evolution. RESULTS: This article presents a case study on teacher-student interactions within a seventh-grade teaching unit on evolution. Video and audio data from the classroom are complemented with data from a post hoc interview with the teacher. Data are analyzed using the qualitative documentary method. Analyses show that the teaching practice can be described as ambiguous and is characterized by a compatibility of scientific and teleological explanations. This results in the reproduction and enforcement of students’ teleological explanations. These aspects of the teaching practice are related to the teaching norms stated in the interview: the norm of motivating students and the norm of transforming teleological explanations into scientifically adequate evolutionary explanations. The results show that in contrast to the interview, these norms cannot be reconciled in teaching practice. CONCLUSION: The relationship between teaching norms and teaching practice is discussed in view of norms in the field of biology education, i.e., conceptual development from teleological to evolutionary explanations, and teleology and anthropomorphisms as a means to promote interest. In this light, suggestions for dealing with teleological explanations are elaborated on, focusing on metacognitive approaches. Furthermore, it is argued that videos and transcripts of classroom interactions also provide rich data for the education of preservice teachers and for professional development.