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 modelling procedures, the approach provides a parsimonious model of growth suited to comparisons between groups.