This paper examines how the National Disability Insurance Scheme’s (NDIS) rapid and unexpected growth has been driven by fundamental design flaws in its original legislation, compounded by weaknesses in implementation. It argues that the rights‑based framework for 'reasonable and necessary' supports lacked clear definitions, financial boundaries and value‑for‑money safeguards, encouraging expansion beyond the scheme’s original intent. 

The paper analyses failures in sustainability, fairness and eligibility assessment, highlights the impact of legal and administrative settings. It outlines a reform agenda to restore fiscal discipline, accountability and a focus on people with severe and permanent disability, including:

• the introduction of independent and standardised eligibility assessments
• clearer legislative definitions of support criteria
• stronger evaluation of therapies and services
• enhanced financial oversight
• a greater emphasis on early intervention to reduce long-term reliance on the scheme.