On the stability of value added indicators

This paper shows how relevant concepts in educational effectiveness can support public policy in order to improve the performance of educational systems. Specifically, value-added indicators and the property of their stability over time is addressed with reference to application to school/teacher improvement. Findings of a longitudinal study developed in Portugal concerning primary education in mathematics are presented. Variance component models are fitted in order to obtain those indicators yearly to class-school units. Results of this study reveal that value-added indicators can be a useful instrument for progressive improvement in education, particularly in countries with high rates of student retention and evasion. The novelty of this paper is to measure value added over a single year rather than all stage of schooling that refers to more than 1 year.