Abstract
In theearlyBOs Mayberry (1981) developed a diagnostic instrument to b~ used to as.sess the van /fiele levels of pre"service primary teachers. The telt which w4scarri~ out iflan interview situation, was desil1ned to examine seven geometric concepts. There has been no report8d attempt to. (a) rerplicat~ this work in Austraiia; (b )c()nsider the items in some alternative format; Qr (t) aIUllyse the validity of the test questions. To address these issues, a detailed teSting and interview program of 60 first year primary.teacher trainees was undertaken at the University of New England. This pape.r considers one aspect of the findings of this study. It concerns the potential for certain aspects of Mayber,y's work to lead to an incorrect assessment of a student's level of understanding in geometry. In particular, four main featureswerefound to account jor .major problems to the test validity.