Applying the Rasch Growth Model (RGM) for the evaluation of achievement trajectories.

Considerable interest lies in the growth in educational achievement that occurs over the course of a child’s schooling. This paper demonstrates a simple but effective approach for the comparison of growth rates, drawing on a method first proposed some 80 years ago and applying it to data from the Australian National Assessment Program. The methodology involves the derivation of a ‘meta-metre’ – a quantitative mode of variation in growth – which permits comparison between groups defined by time-invariant characteristics. Emphasis is placed upon the novel characteristics of the method and the valuable information it can provide. Unlike complex modeling procedures, the approach provides a parsimonious, easily-interpretable model of growth.