The aim of this thesis is to investigate classroom interaction. Of central importance are the following questions; Does gender of pupil, gender of teacher, age of pupils, subject taught and class size have any importance for the classroom interaction? What conceptions of interaction with pupils do teachers have? Data have been collected by two different methods – structured classroom observations and focus groups. The results from the observations study disclose that the gender of the teacher as well as the gender of the pupil has an impact on classroom interaction. The interaction also differs regarding the pupil’s age. The variables pupil gender, teacher gender and pupil’s age together gives an opposite pattern of interaction. Female teachers interact to the same extent with boys and girls when they are young (lower level). When pupils grow older (inter­mediate and upper levels) they interact more with boys than girls. The pattern of interaction for male teachers goes in the opposite direction. When the pupils are young, they interact more with boys compared to girls. The same pattern is true at the intermediate level. At the upper level male teachers interact to the same extent with boys and girls. School subject and class size proved to have a limited impact on classroom interaction. Through categorization of data collected in focus groups, eight different themes were identified. These describe teachers’ conceptions of their interaction with pupils. The themes were large classes, catch individual pupils, boys dominate the classroom on expense of girls, pupils’ needs of interaction with adults, the joy of interacting with pupils, do we use the same language, conflicts between pupils, and to meet pupils with another cultural background. The results from the observations and the focus groups have shown, to some extent different but all-important aspects of classroom interaction. In this thesis two phenomena or questions have been of central importance – gender differences and class size.