In this study we sought to And out how teachers could make assessment fairer for Indigenous students in learning mathematics, given the context of the high stakes of the National Assessment Program Literacy and Numeracy (NAPLAN). Today, teachers are experiencing the full range of demands from their own students who require individual attention, through to system level expectations of improved performances for all students. Many staff experience reform fatigue with limited time for critical reflection and a reduction in support for the use and the analysis of the overwhelming amount of data that has become available in recent years. Over the past three years we worked with teachers in seven schools to gradually refine our research focus to centre on how we might best support teachers in this demanding context with the important outcome of improved teaching and learning of mathematics with particular consideration of how to respond to the cultural needs of Indigenous (Aboriginal and Torres Strait Islander) students. The methodological approach of a design experiment, coupled with a socio-cultural theoretical lens for data analysis, challenged our thinking and our observations of teachers' assessment practice and pedagogy. Most recently, we worked closely with the teachers of the four schools in the final phase of the study to support them to modify their practice to engage their Indigenous students in effortful learning. The main actions we employed included: modelling problem-solving activities; strategic thinking; collaborative learning and employing Indigenous contexts to explicate mathematical terminology; and to decode written assessment tasks in order to facilitate Indigenous students' access to the literacy demands of these tasks. In this article we focus on the role of the teacher in promoting effortful learning in mathematics with Indigenous students. We explore how teachers can promote student mastery and work to improve results in high stakes testing through actively diagnosing and scaffolding student learning. Our research aim required us to critically examine the role of the teacher in effortful teaching to enhance the knowledge and understanding of the Indigenous students when learning mathematics in the specific concept area of problem-solving.