Additives suspected of causing hyperactivity in children have been removed from primary school meals in Conwy.
Children at Ysgol Cystennin in Mochdre try their new menu
The council has said it is the first in Wales to introduce such a ban.
It came after a project at Deganwy School showed children's behaviour and concentration improved when healthier food was served.
Headteacher Dafydd Roberts said: "We noticed over a number of years that children's concentration after lunchtime tended to deteriorate and some of them could be quite excitable and hyperactive."
The school had long introduced a fruit only rule during morning break but still encountered problems after lunch.
But there was a noticeable change in behaviour when jacket potatoes replaced beef burgers on the menu.
Mr Roberts said: "Now the children are much calmer and their concentration has seemed to improve.
"The children have taken to it very well and have a great interest in what's on the menu and in general are very positive too.
"We have an excellent school cook who not only produces the meals well but presents them well and she takes pride in what's on offer which includes more fruit and vegetables."
Parent Fiona Richards, whose children Michael, 11, and Anna, eight, attend the school, said: "Both my children decided to have school dinners because they have improved and there is a variety of food on offer.
"Rather than me saying, 'you shouldn't drink this or you shouldn't eat that,' it's come from a third party.
"They've taken a real interest in what they eat and it's quite educational."
A typical menu now offers roast turkey with stuffing and cream potatoes, jumbo cod fish fingers and chocolate plum cake and white sauce.
As a result of the success at Ysgol Deganwy, Conwy's catering staff have worked with schools, dieticians, suppliers and distributors to source products and ingredients free from the artificial colourings and flavourings suspected of being a contributory cause of hyperactivity.
Carol Davies, Conwy's catering manager, said: "We've been encouraged by the positive response from major manufacturers who have been prepared to modify and revise ingredients and recipes to meet our requirements.
"It's still been possible to create a menu for the 5,000 pupils currently taking a meal which complies with National Nutritional Guidelines; can be prepared within the strict financial targets and most importantly appeals to children.
"School cooks and kitchen staff have made a tremendous effort to ensure the success of the launch across the county's schools.
"It's hoped that due to the success of this initiative that food manufacturers will recognise the benefit of further reducing or eliminating unnecessary colours and additives in their production methods."