The crimes of Britain's 32 worst pupils (who were still allowed back into classrooms)

Some of the children used weapons, including knives and scissors, to attack staff and pupils.

Others made death threats or laid false allegations that threatened to wreck teaching careers.

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How it should be: But well-behaved pupils are being disrupted by 'unteachable' children who are being allowed back into school after being expelled

Despite their appalling records, all the "unteachable" youngsters were allowed back into classrooms after being suspended or expelled.

Most were reinstated by their school's governors or by independent appeals panels. One was as young as five.

The blacklist was drawn up by the NASUWT teaching union, which said new disciplinary powers handed to schools were "not worth the paper they are written on", because heads and governors were failing to use them.

The union's dossier, which is being made available to ministers, records appalling violence ranging from brutal attacks on pregnant teachers to stabbings of staff and pupils.

In one case, boys who bought knives on a school trip to France, and used them to stab a fellow pupil, were allowed back into class.

Other cases include pupils who tried to push children in front of cars outside school and that of a six-year-old who squeezed chilli paste into another child's eye.

One teenager followed a teacher while out shopping threatening: "I am going to murder you".

Despite his age, the five-year-old had clocked up 20 days of suspensions for hitting pupils, throwing equipment and threatening staff.

Chris Keates, the union's general secretary, said: "These figures show that governors are not taking a tough enough line.

"They are not doing the job they need to do with the powers they have been given.

"From a youngster's point of view, if you do something very serious and you are temporarily excluded, you are soon back in school with those teachers and other pupils.

"What is the message to the youngster and the other pupils? You can hit a teacher and verbally attack them and you get a few days off and then are back in school."

In all 32 cases in the dossier, the union balloted members over whether they should refuse to teach the children.

This action is taken when teachers feel they need protecting from a classroom troublemaker.

The votes are also usually a response to the failure of a governing body or independent appeals panel to support a headmaster's decision to expel a youngster.

The boycotting tactic usually prompts the local authority to transfer the pupils to either another school or a special unit.

Mrs Keates said increasing numbers of incidents involved knives and blades.

She said staff and governors must make use of stronger powers to discipline pupils outside school grounds.

"From the Government's point of view, if new legislative powers for schools are not being used when necessary, it brings the law into disrepute and is not worth the paper it's written on," she added.

Jim Knight, the Schools Minister, said: "We have given heads powers to take tough decisions; to exclude where behaviour warrants it, and we support them in using these powers.

"Latest figures show that only 130 pupils who are permanently excluded returned to the school they were removed from, following an appeal."