Healthier school meals could improve children's ability to learn, according to their teachers.

The Scottish Secondary School Teachers' Association (SSTA) has called on the Scottish Executive and councils to do more to replace fast food with more nutritious school dinners.

It said there is a direct link between what children eat in the school canteen and their performance in the classroom.

The SSTA said a significant amount of research shows that foods with high fat, sugar or salt content affect the way the brain works.

Tommy Sheridan: Proposes free school meals

The SSTA, Scotland's second largest teaching union, said the executive should seriously consider improving the quality of food on offer in school canteens as a way of helping children to achieve.

It also said dehydration was a problem for many pupils and easy access to drinking water should be priority.

The SSTA call came the day before the Scottish Parliament debates a bill on free school meals proposed by Socialist MSP Tommy Sheridan.

The executive is opposed to universal free school meals and has said that the cost of such a project, put at �174m annually, would be better spent targeting help at the poorest children.

Earlier this week, a leading health expert said that free school meals for all pupils would make a significant difference to the health of Scotland's children.

Dr David Player said a nutritious midday meal for every school pupil is vital to improving the long-term health of the nation.

The expert, who was the founding director of the Health Education Board in Scotland, published a report extolling the benefits of universal free school meals on Monday.