Schools are paying consultants to fudge Ofsted inspections by unfairly helping headteachers and staff boost their ratings, it was reported.
The education watchdog has long outlawed the practice of allowing schools to stage "mock" inspections, which are considered to give them an unfair advantage.
But according to the Independent newspaper, schools are paying consultantsup to £600 a day to help assess which areas need improvement before the real inspection.
It is thought the consultants could be used to cover up long-standing problems at the country's schools that Ofsted inspectors would ordinarily detect.
An Ofsted spokesman said: "Ofsted has repeatedly said we do not expect, or want, schools to prepare for inspections. Schools should do nothing other than focus on providing a good education.
"Under the terms of their new engagement, Ofsted inspectors will not be allowed to carry out mock Ofsted inspections.
"Furthermore, we have been clear with our contracted Ofsted inspector workforce that they are not allowed to carry out mock Ofsted inspections.
A Department for Education spokesman said: "School inspection is a vital part of our accountability system and improving school standards.
"We have been clear that headteachers do not need to 'prepare' for visits from Ofsted, and have issued guidance that confirms facts about the requirements of an inspection and dispels myths that can result in unnecessary workloads.
"Instead of focusing on inspections, we want teachers to maximise their time in the classroom helping pupils reach their full potential."