In Germany as well as in other countries, there is a great consensus that fostering Students‘ social competence is an important task at school (Frey & Bos 2012). However, it is often stated and complained that schools – especially at secondary level – almost exclusively focus on academic learning and do not pay enough attention to a promotion of students’ social competence. If efforts to foster students’ social competence are made by teachers, they primarily seem to concern those (behavioral) aspects of social competence that are vital for smoothness of academic learning and instruction. Along with this the development of other resp. cognitive and emotional-motivational aspects of students’ social competence is seemingly more or less left to chance (Ludwig et al. 2005, Kunter & Stanat 2003). Thus, one can conclude that there is a mismatch between (supposed) educational goals and actual practice at school. Seemingly schools do not only miss to take all of their opportunities to influence Students’ development in a desirable way, but also risk affecting it adversely (Rathunde & Csikszentmihalyi 2005 a; Lillard 2008).

Against this background, the Montessori approach sometimes is described as a good model for an improvement of traditional school environments – especially at secondary but also at primary level (Ludwig et al. 2005, Lillard & Else-Quest 2006; Lillard 2008). At first glance, that is quite plausible. The Montessori approach aims to promote the development of the whole person, following Montessori academic and social competence are considered as equal goals of education, the Montessori curriculum provides explicit instruction on social behavior, and many characteristic elements of Montessori School environments are supposed to enable resp. promote an acquisition of social competence (Lillard 2008). Nevertheless, a closer look reveals, that to date there is only little empirical evidence on the effectiveness of Montessori schools. Rathunde & Csikszentmihalyi (2005, 343) point out, that “this is especially true” with reference to schools at secondary level and regarding the goal of fostering social competence.

By examining the following research questions we intended to partially fill this research gap, and thereby allow better informed statements whether Montessori Schools could resp. should be considered as good models for an improvement of traditional secondary schools.

1. Are there any indications that Montessori Schools (at the end of secondary level 1) are generally more successful in terms of fostering students' social competence than Traditional Schools? To which extend different Montessori Schools are more or less successful in promoting Students’ Social Competence?
2. If there are systematic differences between Montessori and Traditional Schools, are these differences comprehensive or limited to particular facets of social competence, that are more or less essential for the successful application of specific teaching and learning methods in Montessori or Traditional Classrooms?
3. To what extend the school type and the specific learning environment at Montessori vs. Traditional Schools seem to have an impact on the development of students’ social competence? How important is this impact in comparison to influences of other variables such as family background or characteristics of an individual school?

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