Schools could see their maths scores rise if they timetable lessons in the morning, research suggests.
But students do better in history if they have classes in the subject after lunch.
Researchers found children are better at repetitive tasks early in the day, while tasks that involve evaluation are best left to after lunch.
Scientists from the Royal Holloway University of London looked at academic achievement, class schedules and absence rates at a Bulgarian school over nine years, reports Daily Mail.
The findings show that when teenagers had maths classes earlier in the day, they did better than if they had the same class in the afternoon.
This is because children find it easier to perform repetitive, automatised tasks earlier in the day, according to research.