Pupils who eat a nutritional meal at lunchtime are more likely to misbehave during group-work sessions than pupils who have been poorly fed, a new study has revealed.
But, paradoxically, pupils who have eaten a nutritional lunch are significantly more likely to pay attention to their teachers.
These mixed messages appear in a study - produced by academics from the Institute of Education in London working with the Government-funded School Food Trust - examining the effects of nutritional meals on 146 primary pupils.
The researchers found that pupils who were fed nutritious meals were more than five times as likely to behave well, pay attention and work hard than those whose meals were less nutritious.
"Anecdotes from teachers and parents describe dramatic improvements in children's concentration, behaviour, learning and academic performance when healthier school food is introduced," they said.
Improving school dining facilities also had a positive impact on pupils' ability to behave and work well. However, this was less significant than the difference seen in pupils who had eaten well.
But when pupils were asked to work with each other in groups, rather than to listen to the teacher or work on their own, there was a dramatic shift in behaviour.
Pupils who were fed a good meal were more than three times as likely to misbehave and lose concentration than their poorly fed peers.
The researchers said: "Generally increased arousal in pupils who have eaten a healthier lunch may help to explain the increased off-task behaviours when pupils were asked to work together without direct teacher supervision."
But Rachel Cooke, a nutritionist with the British Dietetic Association, insists this should not deter teachers from feeding pupils properly at lunchtime: "Evidence shows that children need five fruit or vegetables a day, and don't often get it," she said. "So getting a healthy, balanced meal at lunchtime is the way forward. Children are out and about at lunchtime, so hopefully they'll use some of their energy up
"Let's take the positive - eating something that's good for them - and work around the negative. Maybe they can do group-work in the morning."