Capita, the company responsible for criminal record checks which was fined nearly pound;2 million for its failings this week, has left some teachers waiting more than a year to be cleared.
Education supply agencies said they felt the service had improved noticeably since last summer's problems, when thousands of pupils were sent home because of delays in vetting staff.
However, the Recruitment and Employment Confederation said that most agencies were still waiting for responses to some applications made in the two months after the bureau began work on March 11 last year.
Pauline Latham, director of Derby-based Safer Recruitment, said she had more than 10 applications outstanding from March and April 2002 and around 300 others which were more than six months old. "It is as if they lost them in a black hole," she said.
A Home Office spokesman said he could not comment on individual cases, but said that the CRB had reduced the average time it took to process an application from eight weeks to five.
The Government this week revealed that, up to February, it had fined Capita pound;1.8 million for failing to meet targets and planned to recover further damages.
The figures were revealed after Liberal Democrats complained to the Parliamentary Ombudsman about the Government's failure to provide details of the penalty imposed on the company.
A Capita spokesman said the Government had given the company an extra pound;8.4m because of last-minute changes to the application forms which had made them more difficult to process.