The present study examined the impact of teacher team composition on characteristics and attributes regarded as necessary for effective cooperative teaching. The study focused on potential differences between self-selected teacher teams and teams composed by the school administration. The central assumptions were that teachers working in self-selected teacher teams show more positive ratings of enjoyment, shared responsibility, job satisfaction and collective self-efficacy expectations than teachers who worked in institutionally composed teams. In order to investigate these hypotheses, an online survey was created. 321 language arts teachers participated in the survey. MANCOVA revealed significant differences in the dimensions 'shared responsibility' and 'enjoyment with the co-teaching process' , where teachers from selfselected teaching teams showed significantly more positive ratings. These results support the assumption that self-selection of the teammate is helpful for establishing compatible teaching teams, but does not necessarily lead to a higher quality of collaborative teaching.

Scholars have studied collective teacher efficacy mainly at the school level. The present study also focuses on collective teacher efficacy expectations, but it emphasises the collaborative teaching of two teachers working together in one classroom. This study investigates personal, contextual, and systemic factors (e.g. experience, gender, class composition, pleasure with Co-teaching and its standards, knowledge about specific Co-teaching skills, the way how the team partner was chosen, etc.) that may influence collective self-efficacy expectations of Co-teacher teams. For the present study, 264 teachers who were part of a Co-teaching team finished an online questionnaire. Results from multiple regression analysis indicated that team characteristics influenced the subjective evaluation of efficacy expectations in teams much more than individual characteristics or the social context in which Co-teaching teams worked.

Wissen und Handeln. Lehrerinnen und Lehrer verändern ihren Mathematikunterricht 1Summary: Constructivist approaches have been claimed to be appropriate in teaching mathematics. A complex implementation strategy including the teachers' construction of their own lessons and intense co-operation among teachers yielded important changes both in the teachers' subjective theories as well as in their behaviors. The traditional teaching approach is not replaced by the constructivist one, rather, both approaches co-exist simultaneously. As the detailed observation reports by students using the lesson-interruption-method show, the teachers can teach traditionally or constructively upon request, and the differences between the two teaching approaches within the same person are quite substantial. Some conclusions with respect to constructivist teaching and to implementation are drawn.

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