Malmö Studies in Educational Studies nr 73. This doctoral thesis investigatef and describes the design process of two physics teachers and myself in developing and trying out language based learning activities in a first year physics course in two classes in ml urban high school in Sweden. The design process, which goes on for almost three semesters, and these activities are seen as an intervention into the two physics teachers' teaching practice with the aim of contributing to learning and improved practice for them, and in turn, to improved learning of physics for their students. The research questions relate to the design process1 the teachers' teaching repertoire, and to the students' speaking and writing as part of the language based lenrning activities. The background of the thesis is an increased need to high light and to take into account linguistic factors in content area teaching for the reason of linguistic heterogeneity within the student body. Linguistic diversity refers to students having another first langungc tlmn Swedish, the langunge of instruction, and to students being more or less familiar with the specialized academic language used in formal education. The overall theoretical perspective is socio•culturnl, placing an emphasis on language as a mediating tool for meaning-making in situated practices. The empirical mnlerinl mainly consists of field notes and audio recordings from observations of the physics teaching and from the weekly planning meetings but also of sludent texts and audio recordings of students' small group conversations. The teacher group develops nnd tries a number of language centered learning activities1 and their objectives are stated in terms of language tasks to be performed with a specific content. Even though the design process is a collaborative effort, the two physics teachers show difthences in two areas: a) emphasizing speaking or writing aS the main mediating tool in the learning activities, b) creating activities where the students' knowledge construction is either more of a putting together and presenting the content or more of on unpacking and trying it out. This diftercncc might be seen as placing an emphasis on the process towards the goal versus placing it on the film! goal. The student conversations in small groups are oriented towards the content and the topic of the assignment, and they arc cooperative. They also tend to be a matter of accumulating knowledge more than exploring knowledge, which means that criHcal and explorntive features are less prominent The student texts can be seen either ns independent texts or satellite texts, the former intending to state knowledge conclusively while the latter intend to support conversf"ltions. The teacher group tend to plan language centered learning activities towards the end of a content area, and the activities are seen as most relevnnt at points where a move to a more abstract level of knowledge is required. The activities gain a formative function in the teaching process.