This book aims to help the practitioner derive maximum benefit from the use of individual norm-based tests of mental development. It includes, but also goes beyond, an explanation of the psychometric expertise required to use such tests. Beginning with an exploration of the nature of mental development itself, the author explains how the very presence of the assessor impacts on the assessment process both in terms of perceptual idiosyncrasies and in terms of the effectiveness with which the interpersonal dynamics between child, carer and assessor are managed. This is a holistic guide to skilled observation, accurate interpretation, and effective reporting, which equips the reader to derive accurate conclusions in the best interests of the particular needs of the child under assessment.