This paper first reports on the methodology of a study of teacher knowledge for statistics, conducted in a classroom at the primary school level. The methodology included videotaping of a sequence of lessons that involved students in investigating multivariate data sets, followed up by audiotaped interviews with each teacher. These stimulated recall interviews were based on the viewing of edited episodes from the classroom videos. The video and audio data were analysed against a teacher knowledge framework that had been formulated in relation to categories of teacher knowledge and components of statistical thinking. The second part of this paper validates the framework as a useful way of examining the teacher knowledge that is needed for and is used in teaching statistics through investigations. Teacher beliefs about the role of visualisation in context-specific tasks: towards a multi-layered and explicit didactical contract.