Schools are passing on information of their experiences and commenting on the likes and dislikes of particular inspectors.
Some are now even finding ways of objecting to inspection team members, with the most common cause cited as a professional or social connection with the school.
Information is gleaned from the curriculum vitae of inspection teams that are routinely sent to schools. Heads follow up with questions about previous visits and then reach for the phone.
A private discussion group is about to be set up on the National Association of Head Teachers website for heads to file their own inspection reports. Complaints will be lodged with the schools inspectorate following consistent concerns about teams or individual inspectors.
This week, Mick Brookes, president of the NAHT- which wants inspection based on self-assessment - likened the present Office for Standards in Education regime to the Spanish Inquisition.
David Hart, the association's general secretary, said: "It is time for OFSTED to be accountable in the way that schools are requird to be accountable."
Details of the schools' grapevine emerged the week after Martin Stephen, high master of Manchester Grammar School, called in The TES for national league tables of inspectors.
Heads in Hampshire regularly use the council's intranet to ex-change inspection views. About three years ago, the county backed complaints made by three primary schools about the same team.
Essex head Terry Creissen said: "There is a grapevine and it's very important. But some teams are good in one school and bad in another. I had a call from a Cambridgeshire head saying 'I hear you had so and so as an inspector. What are they like, what's the agenda?' They put the school in serious weaknesses. I'm still in touch with the head."
Challenges to individual members of the teams are made to either the registered inspector or the contractor, rather than OFSTED.
Only 3 to 4 per cent of all inspections prompt formal complaints from the school, and most are tackled directly by OFSTED. Last year just five cases went to the independent adjudicator.
OFSTED was not surprised to hear of the grapevine. "It is not something we could stop or object to," a spokesman said.