In 2012 there were 24,474 year 1 to 8 students being educated in the range of Māori medium bilingual and immersion programmes that exist throughout Aotearoa. This figure made up 25% of the total primary school population. To ensure the survival of te reo Māori, and the cognitive advantages associated with bilingualism, Māori medium students need to reach a high level of proficiency in both the English and Māori languages over their time at school. They need to develop their language skills beyond basic conversational competency to academic language proficiency. As well as academic success, Māori medium whānau expect their students to gain a level of competence in te reo Māori that enables them to actively engage in authentic Māori cultural contexts. This is crucial as the interruption to the intergenerational transfer of te reo Māori caused by colonisation means that today Māori medium graduates make up the main pool of speakers who can transmit our language into the future. Substantial research has evidenced effective pedagogies for supporting students’ second language acquisition internationally. However, to date there have been no empirical studies to evidence effective second language pedagogies that can raise Māori medium students’ academic language in particular. This study aimed to bridge that gap by providing evidence of effective classroom practices that can raise Māori medium students’ academic language proficiency, with a particular focus on oral language competency. This action research project aimed to raise a group of Māori medium students’ academic oral language proficiency through the practice of self and peer assessment. The participants were a group of eight year 5 and 6 students being educated in a level one Māori medium classroom in a mainstream school in Southland, New Zealand. Over the 20 weeks of the study the students used a newly developed language matrix of writing outcomes to self and peer assess their learning in their literacy programme. The quantitative and qualitiative results of the study revealed that the confluence of self and peer assessment practices and the new language scaffolds raised the students’ academic oral and written language competency significantly beyond what was normally expected in a Māori medium programme in 20 weeks. The study findings provide an option for those teachers wishing to develop their Māori medium students’ academic Māori language proficiency. The study also highlights the need for further research into Māori language acquisition pathways, to inform Māori medium oral language progressions and associated assessment development.