Private-school proprietors who plan to sell are being advised to keep school staff in the dark until the deal is done.
STC, a confidential school brokerage, says that if news leaks that you are selling, staff and parents may become uneasy, which may damage the business.
Director of STC Peers Carter told The TES: "It unsettles staff if they know the management is changing.
"It can cause defections by the truckload and that is very bad for the business."
He said it was worse for staff to be faced with constant speculation and a barrage of questions from parents than to be presented with a fait accompli.
The company, which handles up to 100 school and nursery sales a year, uses methods such as asking potential purchasers to sign confidentiality agreements and to make discreet out-of-hours visits to keep plans secret.
It advises proprietors to wait until contracts have been exchanged before informing staff and parents of the sale.
But staff should not worry, said Mr Carter. Most owners see the school as their life's work and want to sell it to somebody sympathetic who will build on its success.
And he pointed out that under transfer of undertakings (protection of employment) regulations, the new owner would have to offer existing staff contracts that were the same or better.
But the Association of Teachers and Lecturers said proprietors should consult staff about a sale. Jonathan Restell, national official for independent schools, said: "I can see why there might be reasonable commercial reasons to keep things confidential at the early stages of a sale.
"But we would expect our members to be fully informed as soon as a serious proposal for the school is on the cards."