Although studying the effects of diet on cognitive function in children is of great interest to nutritionists, many have not received the formal training in the principles and practice of assessment necessary to properly evaluate research studies or to design and conduct research themselves. This paper is aimed at such an audience and assumes little prior knowledge of the field. A short description of neural development in childhood is followed by a discussion of important principles of assessment. A level of assessment approach is used to present a selection of widely used cognitive tests organized by cognitive domain and age group. Practical information about the tests is presented in tabular form and a list of useful websites is included.