Lessons at The Ridings school in Halifax could be halted within three weeks if the pupils are not removed, according to Nigel de Gruchy, general secretary of the National Union of Schoolmasters Union of Women Teachers.
He was responding to an announcement by Gillian Shephard, the Education Secretary, that Her Majesty's Inspectors will go into the school on Monday and will produce a full report within the week.
The inspectors will look at standards of behaviour as well as the quality of teaching and provisions for pupils with special educational needs. As many as 180 of the 600 pupils have special needs, and 20 have been excluded from other schools.
Yesterday, Mrs Shephard blamed the local authority, Calderdale, for not acting sooner to solve the school's problems. Only one per cent of its pupils had attained five high grades at GCSE in 1995 and seven per cent in 1996.
"Any local authority which can sit by and accept that one per cent only of the children in a school obtain five A-Cs at GCSE when the national average is 44 per cent, frankly isn't dealing with the problem in a responsible manner," she said.
Mrs Shephard said the resignation of the head and deputy at the school, combined with the fact that many jobs were being filled by temporary staff, had combined with its poor results to convince her that she should take action.
"From the quotes of children interviewed in the course of media coverage of events at The Ridings School, it is clear that children share this view as well," she commented.
"We will not stand by while a badly performing school damages childrens' prospects. "
Two other secondary schools have received similar visits. Blakelaw School, in Newcastle, is now due for closure, and Earl Marshall School, in Sheffield, is undergoing a programme of improvement.
Mr de Gruchy said his union, which represents 35 of the 40 staff, could take action as early as November 12 if the situation does not improve. His members, who have complained of three serious assaults by pupils in recent weeks, will complete a ballot on on Tuesday.
"If lessons continue to be disrupted there will be appropriate action to get rid of these youngsters. We can't go on allowing members to be assaulted and allowing lesson after lesson to be disrupted," he said.
Mr de Gruchy said the union had no "bottom line" on the numbers of children who would need to be expelled or disciplined if strike action were to be averted.
"It would be a surprise if the figure of expulsions were fewer than 20, but we have to examine it over the next couple of weeks and see how the inspectors report and what plans emerge and then make our judgment whether to implement action or whether enough is being done to suspend it."
The Calderdale education committee chairman, Michael Higgins, said the local education authority would work with the inspectors.
"We are disappointed that it's got to this stage, but we are not blaming anybody at all," he said.
"We have not been standing by watching this happen - we have put some support into the school, but it's the strike ballot that has brought things to a head."
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