Education Secretary Ruth Kelly denied newspaper claims 150 sex offenders are working in English schools.
She said 88 people with cautions or convictions for sex offences have not been banned from classrooms.
But the idea that most were now working with children was “just wrong”, she told BBC Radio 4’s Today programme.
On Thursday, Ms Kelly announced that anyone put on the sex offenders’ register in future for offences against children will be banned from teaching.
A central unit will assess cases, taking away powers currently held by ministers.
Ms Kelly said her review of the situation had gone “much further than was asked”.
She expressed “regret” for any “anxiety and concern” that had been caused previously by media revelations that ministers had cleared some sex offenders to work in education.
Ms Kelly said: “The law is changing. In future, anyone who commits a sex offence against a child will be automatically barred from working with children.”
In future, education workers placed on the sex offenders’ register for crimes against children will be placed on the Department for Education and Skills’ list of individuals banned from working in schools.
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