What makes school development successful? Terms such as leadership, participation and professional learning communities are well known. Research has shown that each of these elements contributes its part to the success of school development processes. But there is something that connects all: trust.

The research of the last 20 years has shown the importance of trust for school development. Bryk / Schneider (2002) describe trust as 'Core Resource for Improvement’ and their study laid the foundation for further research in this area.
There are various forms of trust within a school and different people may be affected by it, such as teachers, principals, students, parents, administrative personnel and many more.
This paper will focus on the importance of collective trust within the faculty and its importance for school development processes. More recently, the concept of collective trust has been sharpened and distinguished from the far more commonly used relational trust (cf. Forsyth, et al 2011; Adams et al 2013). Relational trust describes the relationship between individual members of a team, whereas collective trust is defined as "a norm that forms within school role groups", " based on normative conditions and shared expectations" (Adams et al 2013, p 3). It is in fact the whole group and their shared beliefs and norms which are a prerequisite to address developments together and to cope successfully. In the authors opinion, it’s not sufficient if only a few people in the group share common beliefs, but not the whole group itself.

The process of bulding collective trust starts with repeated social exchanges in a group. In the schools, this group is the faculty. The social exchanges lead to a process of social construction and eventually parallels the teachers' beliefs.

In addition, the process is influenced by several contextual criteria, the internal context (such as meetings, style of leadership, coaching), the external context (such as socio-economic status of the student body, media) and the task context (such as the introduction of a new project).

As a result of this process, the faculty starts sharing beliefs and norms and collective trust emerges. Forsyth et al. (2011) show in their 'Model of Collective Trust’, that trust has an impact on many elements in schools: Academic Optimism, Collaboration, Collegial Behavior, Student Achievement, Professionalism – and School Development.

Learning from a recent school development project in Switzerland (project- sls: schools learning from schools, www.projekt-sls.ch), this paper will discuss how important trust can be for all the participants. It is based on a case study of two secondary schools from Greater Zurich Aerea who changed both their learning setting from instructional learning to more self-directed learning. Going through that change process, one project ended up as a success, the other one almost failed. Trust turned out to be an important factor in these two projects.

Tschannen-Moran, Megan (2000): Collaboration and the need for trust. In Journal of Educational Administration, Vol. 39 No.4, pp. 308-331. Bryk, Anthony S; Schneider, Barbara L (2002) „Trust in Schools: A Core Resource for Improvement“. Russell Sage Foundation Kochanek, Julie Reed (2005): Building Trust for Better Schools: Research- Based Practices. Corwin Press. Kelchtermans, G. (2005), “Teachers' emotions in educational reforms: Self-understanding, vulnerable commitment and micropolitical literacy”, Teaching and Teacher Education, Vol. 21 No. 8, pp. 995-1006. Charmaz, Kathy (2006): Constructing Grounded Theory: A Practical Guide Through Qualitative Analysis. Sage. Leithwood, K., Harris, A. and Hopkins, D. (2008). Seven strong claims about successful school leadership, School Leadership and Management, Vol. 28 No. 1, pp. 27-42. Seashore Louis, Karen (2007): Trust and Improvement in Schools. In: Journal of Educational Change, Vol. 8, pp. 1-24. Corbin, J. and Strauss, A. (2008), Basics of qualitative research, techniques and procedures for developing grounded theory, Sage Publications, Thousand Oaks. Goddard, Roger D (2009) „Trust as a Mediator oft he Relationships between Poverty, Racial Composition, and Academic Achievement: Evidence from Michigan's Public Elementary Schools“, Education administration quarterly, Vol. 45 Iss: 2, pp. 292-311. Adams, Curt M & Forsyth, Patrick B. (2009): The Nature and Function of Trust in Schools. In Journal of School Leadership. Vol. 19, pp. 126-152. Forsyth, Patrick B; Adams Curt M; Hoy, Wayne K (2011): „Collective Trust: Why Schools Can't Improve without It“. Teachers College Press. Leithwood, K., Reid, S., Pedwell, L. and Connor, M. (2011), Lessons About Improving Leadership on a Large Scale: From Ontario’s Leadership Strategy, in Townsend, T. and MacBeath, J. (Ed.), International Handbook of Leadership for Learning, Springer, Dordrecht, pp. 337-353. Wayne Hoy, (2012) "School characteristics that make a difference for the achievement of all students: A 40-year odyssey", Journal of Educational Administration, Vol. 50 Iss: 1, pp.76 - 97 Adams, Curt M. (2013) „Revisiting the Trust Effect in Urban Elementary Schools“, The Elementary school journal, Vol. 114 Iss: 1, pp. 11-21