Ministers are reviewing employment procedures after a registered sex offender was cleared for a teaching job by Education Secretary Ruth Kelly.
Ms Kelly said a new vetting system was being developed
The man - put on the sex offenders' register after being cautioned for accessing banned images of children - got a job at Hewett School in Norwich.
He resigned after teaching for eight days last month when police protested.
Ms Kelly said protecting children was her "first priority" and a new vetting scheme was being developed.
Officials would also be reviewing the details of the Norwich case and "further improvements" would be made if necessary, she added.
Making her first public comments on the matter in a statement, Ms Kelly said: "Whilst we do not comment on individual cases, decisions have to be taken on the basis of the evidence and within the legal framework.
"We are already reforming the current system by developing a new vetting and barring scheme with the Home Office and police which will provide better protection for children and vulnerable adults."
Ms Kelly had handed approval for the teacher to work in schools in May 2005.
She had decided not to ban him because she apparently believed evidence he had accessed paedophile websites was inconclusive.
The Department for Education (DfES) Safeguarding Children Unit said Ms Kelly did not believe the man belonged on list 99, the national list of people barred from working with children.
But police reportedly followed strict Home Office guidelines in placing him on the sex offenders register.
In her statement, Ms Kelly said ministers would consider whether there should be greater correlation between the sex offenders' register and list 99.
The Soham case in which Ian Huntley murdered Holly Wells and Jessica Chapman in 2002 lead to recommendations for tighter checks.
Huntley was able to get a job as a caretaker at a college on the same grounds as the girls' primary school despite a string of sex allegations against him.
The National Union of Teachers said nobody on the sex offenders' register should be allowed work in a school.
Margaret Morrissey, from the National Confederation of Parent Teacher Associations, told BBC Radio Five Live the "government haven't learnt lessons" in the past.
"They said they'd learnt lessons over Soham, they assured us parents could be confident everything was in place and, you know, we in our innocence believed them and I know there will be hundreds and hundreds of parents quite frightened across the country," she said.
However, schools minister Jacqui Smith told the BBC the system had stopped the man from working as a teacher.
"Let's be clear. This person isn't working as a teacher. The system broadly saw that that didn't happen," she said.