The purpose of the present thesis is to study whether and how professionals from such different areas as medicine, preschool and school develop and reorganize, through inter-disciplinary focus group discussions, their competence regarding reading-and-writing difficulties/dyslexia. The theoretical framework is based on sociocultural theory of mediated action, focusing on notions such as alterity, intersubjectivity, dialogicality, mastery, appropriation, practical consciousness and discursive consciousness. The data consists of participant field observations, seven individual interviews and fifteen focus group interviews, as well as narratives and written documents concerning collaboration between pre-schools and schools. The method relates to ethnographic and action research. The data is collected over three years. The interviews are audio-recorded and transcribed as close to oral language as possible. The data is analysed with regard to alterity, intersubjectivity, dialogicality, mastery and appropriation, and with regard to professional languages, professional boundaries and domains of responsibility as well as competencies. The results from the individual interviews show that each participant’s conception of dyslexia is closely attached to her or his own field of pracitice. The focus group results show that, over time, the participants changed their conception of dyslexia, and their way of communicating about dyslexia. And, that they thereby deepened their competence on the issue. The written documents show a similar development during the focus group discussions. From hastily scrawled notes they developed into computerised, and well-structured plans of actions for supporting children of special needs. Both the spoken and written data show that inter-disciplinary co-operation leads to the development of inter-disciplinary competence, and a change in organising reading and writing for children of preschool and school.