Nearly 200 school canteens are failing to meet basic food hygiene standards – with many scoring just one star out of five.
Food inspectors say that schools up and down the country must do better.
The worst offenders could now face legal action unless they improve conditions.
New figures from the Food Standards Agency show 73 schools managed only a single star rating. Another 126 were given just two stars under the FSA ratings system.
Inspectors rate food premises from zero to five. One star means they need major improvement while two stars are given when improvements are necessary.
Those named and shamed include breakfast and after-school clubs, children’s nurseries, primary and high schools.
It follows a series of inspections by local authority environmental health departments who looked at standards ranging from hygiene and cooking to how schools managed their paperwork.
The ratings scheme was set up in 2008 to drive up hygiene standards at all places where food is served to the public.
It now covers pubs, cafes, supermarkets, hospitals and care homes as well as prisons.
Food safety experts look at how hygienically food is handled, prepared, reheated, cooled and stored.
They also consider the condition of buildings, cleanliness, lighting and ventilation. A top five rating of five means it has “very good” hygiene standards.
The findings covering 23,000 schools have been published by the consumer website Scores on the Doors.
Scores on the Doors founder Paul Hiscoe said the low ratings of some schools would shock parents.
He said: “If schools get a major improvement required rating they will have letters from environmental health departments and ultimately if they are not satisfied they are cooperating then they could take them to court.”
But he said the ratings scheme had improved hygiene standards at many restaurants, pubs, takeaways and cafes.
He said: “Because of this initiative we have seen big improvements. Major food firms have used this information to improve their compliance. It’s had an impact on providers because they have cleaned up their act.
“Local authorities now have a duty to inform the public about what they find. Until a few years ago this information was kept private between the inspector and the food business.”