Introduction

An ‘indicator’ is simply a statistic describing some feature of the schooling system associated with its performance, such as the average test score of a school, the proportion of drop-outs, or the pupil-teacher ratio. Like most statistics, an indicator derives its meaning from its trend over time, from its variation within a sample, or from comparison to some standard. The standard can be the average value for a set of schools, a predefined goal, or a socially determined standard (Oakes, 1986; Shavelson, McDonnell, Oakes, Carey and Picus, 1987).