Education Secretary Ruth Kelly denied newspaper claims 150 sex offenders are working in English schools.
Ms Kelly expressed 'regret' for parents' anxiety
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.
FIGURES IN FULL
88 known sex offenders have not been banned from schools since 1997
Of these: 10 were cleared by ministers although they were on the sex offenders' list
46 had committed 'very old offences' or only had a caution
Of the 46, there is 'no evidence' of 32 working in education; 13 are still being checked but no reason for concern yet; and one is working in education but not at a school
Police are looking at 32 more people on the sex offenders' list who have a 'potential connection' with education but have not been referred to the Department for Education
Source: Department for Education review
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.
The same will apply for those convicted or cautioned for a variety of "serious" offences against adults.
Education minister Lord Adonis said the ban would include those cautioned or convicted, even if they were teenagers when the offence was committed.
School ban for all people cautioned or convicted of child sex offences
Single banning list for people working with children
Central unit to assess cases, not ministers
Compulsory criminal Records Bureau checks for new school staff and supply teachers used by agencies
School ban for those who commit 'serious' sexual offences against adults
Panel to review past cases of 'partial' restrictions placed on staff
The government's review followed several days of reports of sex offenders cleared to work in schools.
William Gibson, 59, was suspended from Portchester School in Bournemouth last week after his 1980 conviction for indecently assaulting a girl emerged.
It was earlier revealed that a minister had cleared PE teacher Paul Reeve to work at a Norwich school even though he had been cautioned for accessing child porn.
Conservative shadow education secretary David Willetts said it was up to Ms Kelly's conscience whether she was capable of regaining the confidence of parents and teachers after days of uncertainty.
Liberal Democrat education spokesman Ed Davey said confidence had to be "restored rapidly".