Schools could see their maths scores rise if they timetable lessons in the morning, research suggests.
But youngsters do better in history if they have classes in the subject after lunch.
The study, by an academic at Royal Holloway, University of London looked at academic achievement, class schedules and absence rates at a Bulgarian school over nine years.
The findings, due to be presented at the Royal Economics Society annual conference, show that when teenagers had maths classes earlier in the day, they did better than if they had the same class in the afternoon.
For history, the opposite was true.
"The findings indicate that afternoon classes lowered maths test scores and increased history test scores, which relate to psychology and neuroscience research about optimal functioning in different times of the day," the study concludes.
It indicates that by rearranging timetables, schools can improve students' results, said author Velichka Dimitrova.
The findings back up psychology research which has found that it is better to perform repetitive, automatised tasks earlier in the day, while tasks that involve making sense of something are better done later on, it was suggested.
Ms Dimitrova said: "Rearranging school schedules in a more optimal way does not require investment of additional resources and could be a cost-effective intervention leading to improvements in academic performance."