The two boys, 13-year-old Graham Cram and a 14-year-old who has not been named, were both expelled from Hebburn Comprehensive in South Tyneside and were both reinstated by an appeals panel.
In the first case, Graham, who allegedly kicked a teacher, was allowed back to school earlier this month but taught in isolation after staff threatened industrial action. Governors are due to meet to discuss the second case, but the boy is expected to return to lessons.
Yesterday, the general secretary of the union which threatened to strike said that staff were unlikely to take action over the second boy because he had attacked a pupil rather than a teacher.
Nigel de Gruchy, general secretary of the National Association of Schoolmasters/ Union of Women Teachers (NASUWT), said that the law might not recognise action in defence of pupils as a legitimate trade dispute.
"The staff at the school haven't actually come to us requesting any industrial action because this was pupil-on-pupil violence. The kid involved didn't disrupt his class.
"Although in many cases we would like to take action to defend pupils, we need to be certain that the law would allow us to," he said.
The two cases have caused anger among both teachers and parents. Margaret Morrissey, spokeswoman for the National Confederation of Parent Teacher Associations, said the protection of pupils was just as important as that of teachers.
"I would hope the NASUWT or any other union would take this just as seriously it does when a pupil attacks a teacher. We will look with interest to see what its reaction will be.
The school's headteacher, Madelaine Watson, was not available for comment yesterday.
n Disruptive pupils usually blame their classmates for their behaviour, according to research published yesterday. Interviews with 160 children carried out by the National Foundation for Educational Research revealed that most felt either that they had been goaded into bad behaviour or that they did it to impress their friends. Bad relationships with teachers, boring lessons, family problems and bullying were also mentioned as causes. The research officer in charge of the project, Kay Kinder, said that vocational courses which might be more relevant to these pupils could help to improve their behaviour.Reuse content