Pupils as young as 12 were being taught for several hours a week on a range of defence and protection issues, including handling explosives and grenades and shooting guns. The lessons were part of the school curriculum and were compulsory.
Details of the military training for children emerged after British troops broke into two classrooms in a school in Lipljan, 10 miles south of the Kosovo capital, Pristina. The classrooms, which had been shut up with four-inch nails, were full of equipment for hands-on-training.
Among the equipment were devices for measuring radiation and the detection of biological and chemical weapons. There were also a number of boxes of live rounds for automatic weapons.
"We would not be teaching this sort of stuff to cadets back in Britain. We would not think it was appropriate," said the quartermaster Ian Macfarlane, of the Royal Engineers, now stationed at the school which has been taken over by British forces as one of their bases.
He said: "The pupils here were being taught how to make mines, how to lay them and how much cover they should be given once they had been laid in the ground.
"There is nothing to suggest that the children here were being taught anything about leadership or discipline."
The classroom contained piles of exercise books, filled with childish writing and diagrams relating to bomb-making and the breakdown of rocket- propelled grenades. The pupils had written their names inside the front covers.
In one book, the pupil had carefully drawn a cut-away diagram of a Yugoslav land mine showing how to lay and set the mine. Like many other pupils in her class, the work had apparently not been marked.
The classroom also contained a number of textbooks containing military doctrine based on a Soviet model.
British forces, who will take the material away for further examination, say the lessons were taught to all Serb schoolchildren from the age of 12.
Although the idea of children being taught about laying mines might seem repellent to Western eyes, most Yugoslavs would say that there was nothing strange or sinister about it. Yugoslav schools have taught children about military matters since Tito's communist takeover in 1945.
The idea was that all citizens - even young ones - should be able to take an active part in the defence of the country.
The doctrine took on greater significance after Yugoslavia broke with the Soviet Union in 1948, when a Soviet invasion was expected.
"Here was a country where the army was extremely important," said Lt Col Robin Hodges. "I think we were all shocked when we came in and found all of this stuff. We would not think that schoolchildren would need to know how to lay a mine. Clearly here, they thought that they did."