INSPECTORS must avoid a "straitjacket" approach when they examine unusual schools such as Summerhill, according to the Office for Standards in Education's watchdog.
Elizabeth Derrington, Ofsted's complaints adjudicator, will say in her annual report, due this month, that inspectors need to be more flexible when dealing with schools that operate differently or are very small.
She said she found no fault with the official framework inspectors must follow, but had heard from several schools which were upset because they felt they were not being inspected in their own context.
"Schools need to see inspection as a credible product, otherwise it leads to a spirit of resistance. The inspection framework should be treated as a flexible tool rather than a rigid straitjacket."
Earlier this year Ms Derrington adjudicated on Summerhill's complaints about its critical 1999 Ofsted inspection, which nearly led to its closure.
She ruled that inspectors should have acted with greater care and sensitivity and done more to take pupils' views into account.
Summerhill and Professor Ian Stronach, of Manchester Metropolitan University, who has carried out research for the school, claim the adjudication was biased in Ofsted's favour.