A little knowledge being a dangerous thing?: Decile-based approaches to developing NCEA league tables

In recent years it has become increasingly common for New Zealand newspapers and magazines to publish “league tables” comparing schools’ performances in National Certificate of Educational Achievement (NCEA). Since these results strongly reflect socio-economic differences between schools, some media outlets have taken up the practice of arranging school results by socio-economic deciles and/or providing decile “averages”. Although this approach is intended to indicate more clearly “value added” than approaches that do not group schools by decile, this article urges caution towards decile-based comparisons on the grounds that schools have numerous contextual differences that are not reflected in decile ratings. The problem is illustrated here by comparing findings from research in two schools with the same decile rating. We conclude that taking account of deciles does not make judgments about school NCEA performance more defensible, and suggest that the practice be discouraged.