Drawing on concepts developed in actor-network theory and postphenomenology this article shows how material objects in the science classroom become part of epistemic configurations and thus co-shape science education. An ethnographic study on epistemic objects in science education is the basis for the analysis of two of these objects: experimental arrangements and the blackboard. While experimental arrangements configure students as witnesses of the fascinating otherness of material objects, the blackboard enacts students as recorders of semiotic representations. In the interplay of these socio-material enactments scientific knowledge receives its authority in the classroom. The perspective adopted in this article highlights the bodily and sensory dimension of material objects and thus helps to understand how human-technology relations are established. (Contains 7 notes and 4 figures.)