The aim of this study was to describe and analyze the nature of group work through a series of thirteen video taped classroom lessons for fourth grade students. Using a case approach technique, the emphasis was on methodological problems. The study showed that even the investigation of a single mode of instruction such as group work is a highly complicated task. On the other hand, it revealed the fertility of the use of a theoretical framework in an intensive case approach. It was found that pupils' group work is colored with adapted and task-oriented acts. Five appendices are included in the study: 1) interaction variables- rotated factor matrix; 2) test variables, personality trait assessment and sociometric variables; 3) the general course of a group work lesson -12th lesson; 4) Koskenniemi's sociological individual types; and 5) a list of variables. (FDI)