The freak accident occurred as ten-year-old Thomas Brown and two classmates were kneeling on the floor to paint scenery for a school play. A girl bumped into him and he fell forward on to the 12in-long brush held by one of the other children.
A judge ruled yesterday that the risk of injury had been "real and foreseeable" and that two teachers should have done more to protect the boy.
Thomas, now 18, lost the sight in his left eye and suffered a brain injury that has left him with disabilities. A damages action by his father, Christopher, of Birrens Road, Motherwell, is seeking 2.5 million in compensation.
While Lady Dorrian decided North Lanarkshire Council had been liable for the accident, the level of damages will be fixed at another hearing.
The Court of Session in Edinburgh heard Thomas attended Ladywell Primary School in Motherwell. In April 2003, he and two friends were given the long, thin paintbrushes, and were working on the floor because the sheet of paper was thought to be too big for a desk. He lost his balance after the girl knocked into him, and fell on to the other boy's brush.
Thomas was taken by ambulance to hospital and underwent surgery to remove the brush. Doctors feared he might have only a 50 per cent chance of survival. He was allowed home after six weeks but was left with a number of permanent disabilities.
Initially, he used a wheelchair but could now walk, although with some loss of control and poor balance. He had no sight in his left eye, poor concentration and memory, limited reasoning and disinhibition. He had mood swings and outbursts of anger.
It is said Thomas's prospects of finding work are remote due to his "significant cognitive impairment", and that he is unlikely to live independently in the future, and certainly not without professional support.
North Lanarkshire Council said there was no report of any similar accident in any UK school, either before or since Thomas was injured. However, a health and safety expert told Lady Dorrian that "foreseeability is not the same as frequency - an accident might happen rarely yet nevertheless be foreseeable".
After Thomas's accident, a "safety flash" was issued, instructing that art work should not be carried out at floor level. The 12in paintbrushes were shortened and had foam ends fitted. Later, they were replaced by a different type.Shorter, more rounded brushes had been available in the school at the time.
Lady Dorrian said: "The risk arose not from the use of the brush in itself, but the circumstances of its use. In itself, the brush may only carry a possibility of injury. Moreover, when used by an individual child at a desk, that risk may be negligible. Here, the issue was different. It was being used on the floor, the children were kneeling over the paper to work, with the sharp end uppermost.
"They were not only in close proximity to each other but in a situation where it was expected that they would move over the paper, backwards and forwards with the brush in their hands.
"It is the use of the brush in all of these circumstances which required to be addressed. The fact there had been no reported accidents with such brushes would no doubt give the council some comfort in respect of the traditional use of these brushes at a desk or even an easel. The same does not follow in relation to the use to which they were put on the day in question. I think that the risk of some sort of penetrating injury from the brush was a real and foreseeable one."
Lady Dorrian said the two teachers in charge of the class had given thought to some safety elements, but not to others.
"A reasonable person in the position of the teachers would have taken steps to prevent that foreseeable risk of harm to Thomas," she said. "This could have been by the provision of different brushes, which seem to have been available for infants. It could readily have been by allowing the work to be done at a desk. The teachers suggested that it could not be done on a desk, however, I think it could have been done in such a way."