What would happen if you gave children large amounts of sugary food or drink and then ask them to do a maths test? Most parents would react with horror at this scenario, as common experience suggests that food full of sugar leads to hyperactivity and damages any ability to concentrate. But in reality, we can't be sure what would happen. There have been plenty of studies on the effects of malnutrition, mineral deficiencies and the importance of breakfast for the academic performance of children. But not that much on fast foods. One large study carried out by Kerry Tobin showed that children who ate fast foods three or more times per week had significantly lower scores on maths and reading tests than those who didn't. But while this study appears to produce a clear result, actually it's very difficult to be sure. There are so many factors that could influence academic performance that it’s just not possible to be sure whether sugar intake or any other food is playing a central role, or whether other factors are also influencing the result.