Chief Inspector of Schools Sir Michael Wilshaw said "a culture of fear and intimidation has taken grip" at some Birmingham schools.
Sir Michael said the schools regulator's findings at some of the 21 schools reviewed as part of its "Trojan Horse" investigation "are deeply worrying and in some ways quite shocking".
"We found evidence that some headteachers, including those with a proud record of raising standards, have been marginalised or forced out of their jobs," he said.
Ofsted inspectors also found evidence that governors were "exerting far more influence ... than is either appropriate or acceptable".
"A number of headteachers reported that there has been an organised campaign to target certain schools in Birmingham in order to impose a narrow faith-based ideology," Sir Michael added.