This study arises from a project funded by the Scottish Government (2010-12) with the aim of promoting mathematical thinking in the primary classroom. It was set up within a design research framework, which promoted classroom-based action research on the part of participants through a newly developed Masters level course. This took place during 2011-12 with 24 practising primary teachers from four local education authorities in North East Scotland. It uses JATD (Sensevy, 2011) in order to analyse and understand the impact on pupil learning arising from the teachers’ experiences of this course. This framework arises from an understanding of joint action a process of reciprocal semiosis involving the deciphering of verbal and bodily actions (or signs) of others in a particular situation. This process is seen to take place through didactic transactions in particular didactic settings that is conceptualised as a didactic game, as the core of the logical structure of the teaching-learning process. This paper takes a case study conducted by one teacher into the development of mathematical thinking using a topic-based approach on the theme of the ‘Rainforest’, within the context of Scottish Curriculum for Excellence, in order to contribute to the overall aims of the symposium.