This paper deals with an empirical study examining the effectiveness of interdisciplinary teaching in biology and physical education (PE) regarding the students' growth in knowledge. The study was conducted with 141 German sixth form students. In groups, they were taught three hours a week for a period of six weeks. In order to compare the effectiveness of regular lessons with the project, the study uses a test and control group design. This means a test group takes part in interdisciplinary teaching (IdT) lessons while a control group of peers receives subject-related lessons. After being exposed to the different kinds of lessons for a certain time, we then compared the effects on the students' skills in a pre-/post-test. The IdT lessons are designed to complement each other so that the biology lesson supplies explanations for processes occurring in PE, whereas the PE lesson provides a visualisation of the theoretical biology content. In this paper, first the current German curricula requirements as they relate to interdisciplinary teaching will be outlined. After this, the state of research concerning interdisciplinary teaching, methodical-didactic expectations and learning targets will be provided. Following on from this, the data investigated in the course of the study will be presented, such as the study design and measuring instruments. The results of the pre-/post-test will be described and then discussed in the conclusion. They indicate a significant growth in knowledge with the test group (IdT) when compared with the control group (F(1, 113.24) = 126, p<0.01, n[superscript 2][subscript p] =0.43).