Schools should therefore shape timetables around periods when children are most receptive, Barthelemy Trimaglio, a researcher and director of a family agency in France, told the Copenhagen conference, co-sponsored by Children in Scotland.
The weight of evidence about rhythms of learning led to a pound;25 million re-timetabling project in the last two years involving 170 schools, mostly primary, Mr Trimaglio added.
Schools were free to experiment with reorganised days and weeks and many mainstreamed extra-curricular activities into afternoon slots. The majority kept to the standard school week but offered more flexibility around mornings, lunch times and afternoons. Some offered afternoon childcare and others had mixed afternoons.
Mr Trimaglio said: "The Epinal education authority took advantage of the town's plentiful sports facilities to set up a scheme which included timetabling an introduction to more than 40 different sporting and cultural activities. Lessons are taught over five mornings and an afternoon while the local council organises the activities three afternoons a week between 2 and 4pm.
"It requires 200 instructors with different skills and qualifications and costs 2,000 francs (about pound;200) per child. A quarter of the pupils also follow other organised extra-curricular activities between 4.30 and 6pm," he said. Families pay nothing.
Mr Trimaglio added: "The new timetables did not significantly affect academic performance but the children were more motivated towards school, more socialised and receptive to learning."
Children aged between 8 and 11 said they liked the new timetables and the activities on offer, especially when they were grouped together on one or two afternoons. Parents were generally in favour, although some were concerned about effects on basic education.
Mr Trimaglio cautioned: "This drive to mainstream extra-curricular activities into timetables must not make us forget that children go to school to learn. They must not overtire the children because their biorhythms do not stop at the school gate. The child's internal clock must chime with that of the family, which may itself depend on social and economic circumstances beyond their control."
A spin-off from the pilot involving over 100,000 children was the creation of 5,000 casual jobs as instructors.