Schools are allowed to permanently exclude pupils accused of potentially criminal behaviour without proving their guilt "beyond reasonable doubt", the Court of Appeal has confirmed.
A mother, who cannot be identified, last week failed to get her son's academic record cleared by the court after he was expelled for allegedly threatening a teacher with a knife. Her lawyers argued that the way in which the 14-year-old boy was excluded from a school in Waltham Forest, east London, had violated his human rights.
As he had been accused of a serious criminal offence, the school had a duty to prove its case beyond reasonable doubt - as is required in criminal trials - the lawyers said.
They argued that current rules fail to live up to the European Human Rights Convention, which guarantees a fair hearing by an impartial tribunal.
But the court ruled that schools only need to be convinced that the incident had taken place on the balance of probabilities - the lower threshold applied in civil cases.
David Wolfe, who represented the mother, argued legislation introduced in 2004 that lowered the level of proof schools need when permanently excluding pupils should be overturned.
The act has been used in other areas, including prison disciplinary cases, to make the required burden of proof tougher.
But Lord Justice Wilson rejected the argument as the school was not "determining a criminal charge" against the boy.
Mr Wolfe, who will now seek the right to appeal from the Supreme Court, said the decision was "potentially very significant" to schools.
The court heard that the mother had fought the case to have the incident, which took place in 2007, wiped from her son's academic record as she feared it would have long-term consequences for his education and career.
The court heard that the pupil - referred to only as V - and other boys were engaged in a playground fight when a teacher approached. She said V swore at and threatened her and that "she saw a knife in his hand".
However, when V was searched by other teachers, no knife was found and, of eight boys who made statements about the incident, only half said he had been holding a knife.
V admitted he had sworn at the teacher, but denied having a knife.
Lord Justice Wilson confirmed that the headteacher's expulsion ruling was "appropriate", even though the school's appeal panel later concluded that it was only "more probable than not" that the incident had taken place.
John Dunford, general secretary of the Association of School and College Leaders, welcomed the court's decision.
"It is extremely important that courts support headteachers in the very difficult job of maintaining rigorous standards of discipline," he said.
"The balance of probabilities must be maintained as the level of proof because it is not always possible for schools to assemble the evidence that would make it beyond reasonable doubt."