Background/Objectives: Adequate nutrition is considered important for learning, but there is little robust research on the association between diet and learning in school-aged children in industrialized countries. This study investigated the effect of tailored modifications to the food and dining experience in secondary schools on learning-related behaviours. Subjects/Methods: In 2008, 12 co-educational secondary schools in England were recruited. Schools were randomly allocated to receive a tailored action plan and support to modify their food provision and dining environment over a 15-week period (intervention or to control). Learning-related behaviours were systematically observed during post-lunchtime classes at all schools. Observations were made by trained observers using a validated protocol to determine whether pupils were 'on-task' (concentrating and alert) or 'off-task' (disruptive or disengaged). Results: In total, 156 pupils were observed (control n ¼ 58, intervention n ¼ 98) at baseline (12 210 and 20 560 observations, control and intervention, respectively) and at follow-up (16 846 and 23 462, respectively). On-task and off-task behaviours were similar across treatment groups at baseline. At follow-up, intervention group pupils were 18% more likely to be on-task (odds ratio (OR) 1.18, 95% confidence interval ((95% CI) 1.05-1.33) and 14% less likely to be off-task (OR 0.86, 95% CI 0.75-0.98) compared with control group pupils. Conclusions: This study suggests that modifying food provision and the dining environment can improve learning-related behaviours of secondary school pupils in the post-lunch period. This finding supports ongoing investment and interventions by local authorities across the United Kingdom to improve school food and lunchtime dining facilities.