Adolescents who eat breakfast regularly perform better academically than those who skip breakfast. Nutritionists have long emphasised the importance of breakfast for concentration and cognitive function. A five-year longitudinal study found that students who ate breakfast at least five times per week scored on average 12% higher in standardised tests than those who rarely ate breakfast. The researchers noted that eating breakfast provides essential glucose to the brain after the overnight fast, enhancing mental performance throughout the morning. Schools struggling with poor academic results should therefore introduce free breakfast programmes. This intervention would be particularly valuable in disadvantaged areas where students are most likely to arrive at school without having eaten, addressing educational inequality whilst improving overall attainment. Which one of the following best identifies the flaw in the above argument?