The aim of this thesis is to better our understanding of the relationship between physical education and health as a school subject and the school's overall mission. Drawing on an educational perspective, the intention is to interrogate students' perceptions of knowledge, learning and assessment in the subject. With this thesis, I want to contribute to the ongoing discussion about what constitutes knowledge in physical and health and open up for reflections on alternative perspectives on knowledge in the subject. The thesis is a compilation consisting of three empirical studies presented in four articles, study one and the first two articles are also part of my licentiate thesis. In study two, two classes at an upper secondary school were followed during their physical education and health classes for one whole school term. The data in study two consists of interviews, observations, informal conversations and teacher-student grade discussions. Study three comprises observations and conversations with students from two classes participating in six lessons each on ball games.The data analysis in both study two and three are based on non-affirmative theory where both subject-specific knowledge and generic knowledge are central. The analysis shows that the students perceive that they learn subject-specific knowledge as well as generic knowledge but, for the most part, reproductive and affirmative learning is associated with subject specific knowledge. However, the studies also show that the students may use this affirmative (sporting) knowledge in a final individual “healthproject” and somewhat alter the reproduced and affirmative content, to achieve their personal health goals and this learning may then be seen as more non-affirmative. At the same, some students are not able to achieve this reproductive and affirmative learning, which can mean that their knowledge “toolbox” is more limited for the final health project and, by extension, health in a lifelong perspective. In order to enrich and enhance the educational outcomes for students in physical education and health, the pervasiveness of reproductive and affirmative knowledge needs to be challenged by a more non-affirmative way of thinking.