Many children eat a diet which supplies a higher than recommended amount of nonmilk extrinsic sugars and saturated fatty acids. The school setting is often targeted for nutrition intervention as many children consume food at school. In Scotland, attempts have been made to improve the nutritional content of food in schools and attention has now turned to food and drink available “beyond the school gate.” This paper describes the development of a module on food and drink purchasing behaviour. The Food Purchasing Module was designed to collect data, for the first time, from a representative sample of children aged 8–16 years about food and drinks purchased on the way to/from school, during break time/free periods, and at lunchtime, from outlets around schools. Cognitive testing of the module highlighted that younger children find self-completion questionnaires problematic. Older children have fewer problems with self-completion questionnaires but many do not follow question routing, which has implications for the delivery of future surveys. Development of this survey module adds much needed evidence about effectively involving children in surveys. Further research exploring food and drinks purchased beyond the school gate is needed to continue to improve the nutritional quality of children’s diets.