This paper will present an ongoing research project in a Swedish national programme for cooperation between schools and universities (www.kau.se/ulf ). The aim is to provide knowledge regarding how teachers plan and prepare lessons (PaP) in different subjects so that those techniques can be modelled. Further, by comparing different subjects, we will also learn more about the way in which disciplinary boundaries affect the planning process. RQ: How does collegial cooperation affect the practice and the quality of teacher planning and preparation? PaP is vital for high-quality in teaching and thus for student learning (Hattie, 2008; Mertens et al., 2010). Nevertheless, the infrastructure to support PaP is often poorly developed. In Sweden, as in many other countries, PaP is mainly the responsibility of individual teachers, disconnected from the local school organisation (Darling-Hammond & Rothman, 2011; Ellegård & Vrotsou, 2013; OECD, 2020). Indications of deficiencies in such infrastructures include fragmentation of time for planning, absence of functional collaborative settings, lack of routines and relevant input of new knowledge (Nordgren et al.,2019). This project bring together the fields of subject didactic (e.g. Hudson, 2016) and school development (e.g. Jarl, Blossing, & Andersson, 2017). We argue that PaP is a key to school development and that subject specific knowledge and skills associated with good PaP should be at the centre of teacher professional development (cf. Carlgren, 1999; Deng, 2018) to meet the challenges having creativity, literacy, and critical thinking as central aspects of teaching.In our presentation we will discuss how possibilities and restrains in the collegial setting affect the subject-oriented planning teams. We draw on data from planning team meetings (audio recordings, planning documents, etc.). Subject specific, as well as generic variation in the planning teams’ activity enhance our knowledge on how such designated communities can support PaP.