Within the framework of a participatory action research approach, teachers and their students were accompanied scientifically with a focus on Montessori pedagogy and music in an upper secondary grammar school for three years (from 2012-2015). Based on attitude- and self-efficacy-theories, inclusive instruction as well as agent-based research, the aim was to examine the implementation of an inclusive learning - and school-culture at this grammar school – an institution which is part of the highly selective education system at secondary II level in Austria. It has been possible to reconstruct the understanding of teachers concerning inclusion and conceptions of man as well as their selfefficacy of competences to teach in an inclusive environment by means of qualitative and quantitative data. To examine attitudes and selfefficacy of teacher competences, international and national tested scales SACIE-R (Sentiments, Attitudes and Concerns about Inclusive Education-Revised) and TEIP (Teacher Efficacy for Inclusive Practice) were used in a German version. Furthermore, the empirical survey was extended by a webbased national questionnaire for teachers in different types of schools, from primary to secondary level (n= 427) to allow comparative analysis. Interviews, which were evaluated content-analytically and ques-tionnaires for parents (n=37) and students (n=19) offered an indepth insight into everyday educational practice from different perspectives. The synopsis of the result shows, that it was possible for a rather young team of teachers with very positive attitudes towards inclusion, to implement a supportive and vivid learning - and school culture. Nevertheless, the efforts of the teachers did not exceed the system limits. The development towards a ‘school for all’, a logical consequence of theoretical approaches concerning inclusion, was not discovered. The current research is verifying the corefindings of inclusive - and agent-based research. Further findings can be related to the selective structures of the education system in secondary II.