Olympic sprinter Allan Wells saw the new scheme off to a flying start when he joined the dinner queue at Aberhill primary in Methil.
Alex Thomson, who chairs Fife's eduction committee, said: "Action had to be taken if the school meals service was to survive. A great deal of money is brought into education from school meals and jobs could have been lost if the service had gone under."
He added: "I don't think it's bribery. It is an incentive to encourage children to eat nutritious meals which the school provides rather than go to the chip shop. We were faced with making a combination of cuts and generating income in terms of the budget and one way is to increase school meal prices. Unfortunately when you increase prices there can be a reaction and demand is reduced. This is one way to ensure it remains and increases."
Fife serves 25,000 meals a day and the annual turnover from the service is Pounds 875,000. At 90p meals are the second cheapest in Scotland.
Nearly 30 sponsors have donated cash and prizes, Mr Thomson said. "This is quite innovative in terms of the private sector becoming involved."
But he added: "I would have preferred not to have done it to be absolutely frank. Faced with the situation we had which is a direct result of Government policy we had to make a combination of savings and income generation of more than Pounds 4 million in the education budget in this financial year. We were able to reduce the cuts to Pounds 2.6 million but had to ensure that numbers taking school meals kept up."
Mr Thomson continued: "It is also about encouraging children to eat good nutritious meals. In many areas of Fife children come from homes where there are high levels of unemployment and low incomes and often the school meal is the only square meal they will get in the day."
Hazel Gordon, Aberhill's headteacher, welcomed the scheme. "We have 50 more for lunch today than we normally do."
Allan Wells, who had school dinners when he was a pupil at Liberton High School in Edinburgh, said: "Kids who have school lunches benefit from it later in life. I think the scheme is a great incentive for them to eat meals with less sugar and less salt, something that athletes are very aware of in their diets."