Children at one of Bradford's most under-achieving schools were unknowingly taught last term by a violent robber.

Steven Gray, a teaching support assistant at Bradford Cathedral Community College, managed to conceal the fact he was awaiting trial for robbing a 94-year-old great-grandmother.

School leaders believed he was a "decent person" although he had also failed to reveal that he had been forced to abandon his attempt to become an Anglican minister six years ago when he was confronted about his 'inappropriate' behaviour.

Appalled staff discovered the dreadful truth when he took leave and they received a phone call saying he would not be back - because he had been sent to jail.

He was found guilty of robbery at Newcastle Crown Court and handed a seven-year sentence by Judge Tim Hewitt last week who called him "cowardly" and "particularly despicable".

Gray, 29, of Cruddas Park, Newcastle, had worn a cassock to pose as a priest when he called at the home of the 94-year-old woman in Newcastle in July last year.

He offered her chocolate but turned nasty when he spotted her wallet and knocked her to the ground before running off with £30.

David Kershaw, the new head teacher at BCCC, said everyone was shocked to find out Gray was a violent criminal.

"He was supplied by an agency and the school took it on good faith that the appropriate police checks had been carried out," he said.

"That is why schools pay agencies a lot of money, to do the checks."

Gray was supplied to the school in October as a Learning Support Assistant, which meant he carried out group work and individual work with pupils and performed a similar role as a learning mentor.

"Sometimes he would take a lesson, with the teacher there," said Mr Kershaw, who added that he was not placed at the school as a fully-qualified classroom teacher.

"We were all shocked - if he's done things like that it's pretty dreadful. He struck me as a decent person. He went on leave, then we had a telephone call saying he was going to prison."

Ian Davey, of the Bradford branch of the NASUWT teaching union, said: "This has been our fear all along with agencies. We assume they do proper police checks, but do they? I think this should be publicised to all schools and local education authorities - some agencies aren't doing their job.

"Some are obviously more interested in the money than the safety of children."

Ian Murch, of the Bradford branch of the National Union of Teachers (NUT) added: "It's a bit worrying that people can slip through the net, the education authority and the Diocese need to tighten up."

A spokesman for Education Bradford, the privatised education authority, said: "Because the quality of agencies is variable, our advice to all schools is to demand to see all references and police and child protection checks - not to take it on trust.

"Anyone can set up an agency that will supply people to be at your school."

BCCC has 1,200 pupils aged 11 to 18. School performance league tables published in December showed it had alarmingly low GCSE results with only 5 per cent of pupils achieved the standard benchmark of 5 A-C grades, making it the fourth worst in the country.

The Government has threatened to close schools which have fewer than 20 per cent of pupils reaching that target.

Previous head teacher Jo Jones resigned in December.