The case of Erica Johnson suggests teachers may still face excessive delays to be cleared to work with children despite efforts by the bureau to sharpen its act.
The bureau was set up in March to check the suitability of staff to work with children.
Miss Johnson, of Poole, Dorset, applied for a police check through supply agency Teaching Personnel on April 2 but was not cleared until last week - five days before term ended in Poole.
She said: "I have lost a term's wages. I had budgeted to work that term and make the money last all summer."
Miss Johnson estimates she would have made pound;500 a week as a supply teacher after leaving Shillingstone primary, Blandford Forum, Dorset, in April.
She said: "If I had known I would not have given up the job because it has been hell the past few months. I had been through police checks before but this new way of doing it means those do not count."
In May, the CRB brought in a fast-track procedure for teachers. Staff can teach after a quick check of List 99, the register of those convicted or suspected of child abuse. A full vetting is carried out later.
The checks came after agency Select Education complained just 750 of 2,300 of its teachers had been cleared. Select is now happy with clearance times.
A bureau spokesman said every teacher application made before June 18 had a List 99 check. Fast-track checks were taking one to three weeks, though there was still a backlog for full checks.
However, nursery nurses do not get these checks and there are fears some nurseries may have to close as they cannot get cleared staff.
Jean Gemmell, general secretary of the Professional Association of Teachers, said nursery staff were "disaffected" at delays of up to four months and many were finding alternative work.