Purpose: This paper argues that in a well-organised school with strong leadership and vision coupled with a concerted effort to improve the teaching performance of each teacher, student achievement can be enhanced. The purpose of this paper is to demonstrate that while macro-effect sizes such as "whole of school" metrics are useful for school leaders in their professional development roles, there are important micro-conditions that can be uncovered in a more detailed analysis of student achievement data. Design/methodology/approach: Evidence of student achievement in a variety of standardised and non-standardised assessment tasks was subjected to examination in a "post hoc," case study design. The assessment tasks were the South Australian Spelling Test Waddington Reading Test, a school-wide diagnostic writing task, teacher running records and National Assessment Program for Literacy and Numeracy. Performance in selected classrooms was compared on these tests utilising a variety of parametric quantitative statistics. Findings: School-based reform initiatives require external criteria on which to base decision making. Without such criteria based on data and the capacity to interpret it, interactions in the school culture have unanticipated consequences that have the potential to neutralise school improvement strategies. Further, findings suggest that fewer but sharper and quicker data collection tools are more valuable in such teacher decision making, but these require expertise to produce and interpret them. Research limitations/implications: This paper provides insights from one school, but the reported data are embedded in a sustained five year school reform programme. Practical implications: This paper documents a whole school organisational reform model devised by a school head and leadership team to improve student academic performance. The paper offers a process for developing a data-based school reform strategy for professional development to enhance both student achievement and school outcomes. Social implications: The paper outlines a model for school reform that is focused on all students increasing their academic outcomes. By emphasising collaborative teacher work based on research-justified teaching approaches, the model shows that social inequalities can be reversed. Originality/value: The paper outlines a whole of school reform model focused through a combination of distributed leadership, data-driven decision making, within a context of a coaching, mentoring and feedback regime for teachers. Together this model is an application of theoretical ideas to school reform.