Objective: This study describes an evaluation of validity and reliability measures in a questionnaire designed to assess knowledge of applied nutrition in children participating in an after-school care dietary intervention programme being undertaken in an area of high social disadvantage. Design: Three domains were assessed: Knowledge of Applied Nutrition (KN), Knowledge of Food Preparation (KP) and Perceived Confidence in Cooking Skills (PC). Four pilot studies were undertaken to determine item reliability, test-retest reliability, discrimination and difficulty indices, and content, cognitive and face validity. Setting: Primary schools in Dundee, Scotland and Newcastle upon Tyne, England. Subjects: Ninety-eight children aged 11 years. Results: The final instrument comprised 36 questions (18 KN items, 9 KP items and 9 PC items) presented on four sides of paper, which could be self-completed in less than 15 minutes. Question formatting included open and closed structures (KP) and multiple choice (KN and PC) items. All knowledge questions could be answered correctly by 5 to 95% of the target population, with discrimination scores ranging from 0.06 to 0.83. Retest reliability scores were significant (KN 0.458, P <0.001; KP 0.577, P <0.001; PC 0.381, P <0.001) and internal reliability (Cronbach's alpha) of each component was also significant. Conclusion: The test meets basic psychometric criteria for reliability and validity and forms a suitable instrument for measuring changes associated with intervention work aimed at improving food and dietary knowledge.