Group work is used as a means of learning at all levels of most educational systems. However, teachers often use group work without considering its "pros and cons." Such a mode of non-reflected application may sometimes end up in positive experiences and learning, but the likelihood is that the outcome will be the opposite. The aim of this qualitative study is to address students' experiences of collaborative group work, that is, when working as a group. What features do students emphasise in their experiences and descriptions of constructive and destructive group work? A prime aim is to give the students a voice in the matter. Data were collected by means of six focus groups with students aged 13-16, and a qualitative content analysis was performed. The originality of this research is three-folded. First, it discloses what students consider as important requisites for a successful group work. Their inside knowledge about classroom activities end up in a list (a taxonomy) of crucial conditions for high-quality group work. Second, the conditions mentioned by the students have all been confirmed by recent scientific research. Thus, thirdly, the present study may provide teachers with evidence-based knowledge about successful group work. (Contains 3 tables.)