Lancashire County Council has now suspended the supply of all frozen processed beef products to schools.
The move was taken after its own scientific tests carried out in light of the horsemeat scandal cast further doubt on the reliability of food labelling.
The county council is one of the few councils in the country able to conduct its own laboratory tests on the DNA composition of meat products.
It chose to test for traces of horsemeat in all the frozen processed beef products supplied to its schools,. two products tested positive.
The first was a pre-prepared cottage pie used in 10 per cent of primary schools and the second was a Halal beef burger, which had been available at four schools in the county.
All affected schools have been contacted and informed.
Frozen processed beef products only make up a small proportion of the menu, as most school meals are prepared using fresh beef from a local supplier, so pupils will continue to have a wide range of food to choose from.
County Coun Geoff Driver, leader of Lancashire County Council, said: “It is frankly appalling that we have found horsemeat in two products which were supposedly 100 per cent beef.
“These products came from manufacturers who not only carry all the correct certification but who also recently provided us with written assurances their products did not contain horsemeat.
“With children returning from half term break we feel we have no choice but to withdraw all frozen processed beef products as a precaution.”