Children with Down syndrome can and do learn important mathematics and increasingly, this is occurring in regular school classrooms. The research literature offers little about the practices of effective primary school teachers who are including children with Down syndrome in the teaching of mathematics. In this paper we present findings from a project that followed teachers' journeys through a school year as they taught mathematics in primary classrooms including a child with Down syndrome. In particular, we focus on one aspect of the project: the nature of the teachers' practice and the specific challenges that emerged during teaching and planning. Data were collected through classroom observations, interviews with teaching team members and examining learning artefacts such as work samples and reflection journals. Classroom experiences in such contexts often require adjustments both in the planning and in the implementation. Vignettes illustrate such adjustments and provide insights into the teacher decision-making involved. Themes that emerged from analysis of the data are discussed. These themes were based on researcher reflections and meetings following each round of observations and were reported back to the teachers for verification. We explore the themes, reflecting on current policy influencing inclusive education in Australia and internationally, highlighting challenges that emerged in seemingly straightforward concepts. Our aim in this paper is to explore examples of an innovative approach to mathematics education for students with Down syndrome--the technique of teaching all students the mathematics from their year level, with adjustments. The careful study of the practices of teachers offers implications for effective inclusive mathematics education for the diverse classrooms that are increasingly the norm across Australia and around the world.