Their suspicions were confirmed when the Government announced that, of the 88 convicted sex offenders who had not received permanent bans, only one was still involved in education and he was not teaching.
Mick Brookes, general secretary of the National Association of Head Teachers, said his members agreed the Government should improve national vetting systems.
But he said most were very confident about the policies in their own schools. "I received 180 emails today," said Mr Brookes, "but not one was about this".
The NASUWT teachers' union said it was concerned that some local authorities were "grossly over-reacting" to the furore.
Knowsley and Hull have ordered their schools to re-check all the criminal records of all their staff. Both councils said they had made the decision before the recent controversy.
However, Chris Keates, general secretary of the NASUWT, said: "I cannot begin to quantify the distress such panic measures could cause and the burdens this will place on schools."
The TES reported last week that many teachers felt more concerned about pupils who were on the sex offenders' register.
Courses by the NSPCC have helped reduce reoffending among young sex offenders, who have often been abused themselves, but teachers said it was unclear what special support their pupils were receiving or how other students were being protected.
A teacher at a secondary school in the Midlands said: "One of my pupils was on the register and was constantly threatening girls with rape and threatening female teachers. But he had little or no extra supervision in lessons and was allowed unsupervised breaks at lunchtime. That's an outrage whatever way you look at it."