The overarching aim of this thesis is to probe more deeply into how col­laborative writing can help to socialise students in a writing practice. More specifically, the thesis deals with lab report writing and the relationship of three students with different backgrounds to the educational practices of a university department. The three students differ in language background, previous higher education and vocational experience. The material comprises recordings of student discussions while writing lab reports in a group. The students and their lab report writing in different group con­stellations has been followed longitudi­nally for between two to four semesters. In addition the development of the lab reports over time has been studied, as well as teachers’ comments on them. Student acquisition of the genre is linked to internal textual criteria (textual aspects) and to extratextual criteria in the educational context. In view of the study’s focus on group collaboration a socio-cultural per­spective has been adopted as a frame. A model developed by Storch (2002) based on Vygotsky’s role relationships between expert and novice is used to shed light on how the students resolve problems related to the writing task through group discussions. The results show that the students’ backgrounds play a role in the creation of their profiles in the collaborative writing groups. The student with a second-language background often seeks support, not least where linguistic correctness is concerned, and cites what teachers say as arguments. The student with prior experience of academic writing appears to be a seasoned writer, for instance by daring to deviate from instructions and teachers’ directives. The third student uses his professional experience of writing lab reports in discussions to gain acceptance for his ideas.