Education is a fundamental human right. For some children their right to education is denied when they are removed from school on disciplinary grounds. New Zealand Ministry of Education data shows substantial variation across schools in their rates of formal discipline measures. Additionally, there is evidence of children being unlawfully removed from school on disciplinary grounds. Responding to suggestions that principals may be unaware of the relevant law, this socio-legal, mixed methods study explored principals’ understanding and application of laws relating to student discipline. During phase one a survey was developed to explore principals’ familiarity with the relevant law. It was completed by 76 New Zealand secondary school principals, with the results indicating wide variation in principals’ familiarity with laws relating to student discipline. The survey results informed the selection of participants for phase two, which involved interviews with 16 principals from throughout New Zealand. A key feature of these interviews was the use of vignettes involving student discipline scenarios. The themes developed from the interview data highlighted variation in principals’ understanding and application of the grounds for removing students from school and in the exercise of their statutory discretion. The implications of the study results are discussed with a particular focus on children’s rights. Recommendations are made for law and policy reform, along with enhanced data collection and compliance monitoring. To support the translation of law into practice, suggestions for professional development are detailed. These recommendations are timely given the recent introduction of a requirement for the Minister of Education to issue principal eligibility criteria and the forthcoming establishment of a Leadership Centre.