The authors describe a reform effort in which characteristics derived from High Reliability Organization research were used to shape whole school reform. Longitudinal analyses of outcome data from 12 Welsh secondary schools indicated that 4 years after the effort was initiated, student outcomes at the sites were strongly positive. Additional quantitative and qualitative data, gathered 5 years after the end of the intervention, indicated that the majority of the schools continued using the high reliability principles and continued making strong academic progress. Results are discussed in terms of the original High Reliability Schools model, systemic effects, and sustainability. (Contains 4 tables and 6 notes.)