The approaches to teaching and learning mathematics in Australian preschools and schools can be quite different. These differences arise from what can be termed different ‘cultures’ within the prior-to-school and school settings. Even the first years of school can be characterised by teacher-centred, syllabus-driven lessons and written, group-based assessment while the preschools tend to adhere to their child-centred, play-based approaches. The result of these differences can be a hiatus in the children’s mathematics learning and the teachers’ assessment of this learning. This paper reports on one attempt to bridge this gap, not, as so often happens, by ‘forcing down’ the primary school curriculum into the preschool but by maintaining a focus on appropriate learning approaches in this period of the children’s lives. The Southern Numeracy Initiative was established in 2003 in high schools, primary schools and preschools situated in the southern suburbs of Adelaide, South Australia. Its general aim was to improve mathematics and numeracy outcomes through a sustained, collaborative program of professional development and action research, particularly in the areas of pedagogy and assessment. This paper reports work done with preschool educators as part of SNI. It traces how ‘powerful ideas’ in mathematics were identified in current preschool practice, how they were linked to the Developmental Learning Outcomes in the mandatory curriculum documents and how the technique of learning stories (narrative assessment) was established as a valid assessment regime compatible with key principles of preschool education.