Developed in New Zealand some twenty years ago, kaupapa Māori has had a successful impact in education, notably in Māori-medium settings such as kōhanga reo, kura kaupapa Māori and wharekura. However, in mainstream educational settings, where the vast majority of Māori children continue to be educated, achievement disparities between Māori and their non-Māori peers persist. This article focuses on Te Kotahitanga, a large-scale kaupapa Māori school reform project that seeks to address educational disparities by improving the educational achievement of Māori students in mainstream schooling. Experiences with implementing Te Kotahitanga would suggest that reforming mainstream educational practices along kaupapa Māori lines is not easy. This article examines three main impediments encountered in attempts to implement the Te Kotahitanga project in mainstream schools: confusion about the culture of the Māori child; uneven implementation of the project; and problems with measuring student progress. For the project’s aims to be realised, professional development needs to be ongoing, iterative and responsive.