Different Growth Measures on Different Vertical Scales

Abstract

Vertical scales have been used by testing programs for decades to facilitate the tracking of student performance over time. With the recent emphasis on the measuring of student growth for accountability purposes, scores from vertically scaled tests have been used to evaluate school or teacher performance. Because there are different types of growth measures and there are also different ways to construct a vertical scale, it is important to understand the impact of the vertical scales on various growth measures for important educational decisions. Based on some mathematical relationships that have been shown to exist among certain growth measures and with the use of empirical data, this study investigated the impact of different vertical scales on the relationships among simple gain scores, residual gain scores, and three growth measures based on conditional status percentile ranks (CSPR). Results showed that the correlations between simple gain scores and the rest of the growth measures were affected by the extent of scale expansion or scale shrinkage across grades.