There is an increasing focus on teachers' professional learning communities, in Sweden as well as internationally. Collegial learning, however, is not a success factor per se. Often, collegial learning is limited to include collegial work, with focus on activities rather than a changed mindset (Katz & Dack, 2014). There is still a lack of research in how teachers learn in professional learning communities (Meirink, Meijer & Verloop, 2007) and in how these collaborative settings can improve teacher practice (Darling-Hammond & Richardson, 2009).

There is also a demand for research that studies teachers 'professional learning communities from a micro-perspective, taking into account not only what the participants say and do, but also the local and institutional context and the history of teachers' work (Little, 2002).

The research topic in this paper is about teachers' professional learning practices, with a specific focus on how teachers themselves, and with the help of a facilitator, act in a way that enable and/or constrain individual and collegial learning. The overall aim of the study is to understand a professional development practice, in the shape of teachers' collegial conversation practices, from a relational perspective. This involves a site ontological perspective (Schatzki, 2005), where the dynamic relationship between what is happening and the context where it happens, is put to the fore.

In this paper, the theory of practice architectures (Kemmis & Grootenboer, 2008) is used as a theoretical as well as a methodological and analytical tool to study teachers' collegial conversation practices, how they relate to local and national contexts and how these enable and constrain the professional development in terms of individual and collegial learning. Through the analysis, specific arrangements that shape and prefigure the professional development practice are identified, but the analyses also look into how this practice is shaped by the participants.

The study is designed as a case study, the case being an independent school company with four schools in four Swedish municipalities. All mathematics teachers at the four schools are participating in the government financed professional development program "The Boost for Mathematics", based on collegial learning, during two years. The sample is strategically chosen and has been based on the category critical cases of the type most likely cases, in line with the hypothesis that the selected school organization should constitute a particularly favourable case in terms of the structure of the professional development program. Data has been collected during three years and consists of sound recordings and observations of collegial conversations, documentation from collegial meetings and teachers' individual reflections.

The results show that the professional development practice, in terms of the teachers' collegial conversation practices, is held in place and formed by practice architectures that are related to the school company as well as to the professional development program. The results also show that the participants in the collegial conversation practices, the teachers as well as the facilitator, act in different ways that enable individual and collegial learning. These actions can be related to the practice architectures of the specific site where the professional development practice unfolds.

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