The SSTA called on the Scottish Executive to do more to ensure that nutritional food is served in secondary schools.
Annette Ferri from North Lanarkshire, one of the leading voices in the SSTA's campaign over the effects of junk food on learning, said: "We didn't need Jamie Oliver to tell us about the state of food in Scotland's schools, because we said it first."
Unlike primary schools, there was no means of monitoring the standard of food being served in secondary schools, Mrs Ferri said. Research in 2002 had shown that children's diets were too high in salt, sugar and fat.
"These figures remain alarmingly high."
Despite the Executive's "hungry for success" strategy, the reality was that the healthy option in schools was often unappetising and of poor quality, and children were still being served processed foods such as burgers and sausage rolls.
Mrs Ferri claimed there were wide variations in the money allocated to school meals in different authorities. "You can't get quality food at some of these prices," she said. "There are still too many schools serving poor quality food. All processed foods should be removed. Children's health should not depend on a postcode or per capita allowance."
The conference backed a motion unanimously encouraging the Executive to ensure that the necessary funding was deployed by all Scottish authorities.