Four private schools are facing fines of £70,000 each for fixing their fees.
Lancing College, Eastbourne College, St Leonards Mayfield School and Worth School near East Grinstead are among 50 fee-paying independent schools to admit price fixing to the Office of Fair Trading (OFT).
The exemption of schools from competition law ended in March 2000.
Under a deal with the OFT, the schools will admit to sharing information about the fees they intended to charge parents for the academic years 2001/2 to 2003/4.
The information was swapped via a survey sent to all schools in breach of the Competition Act 1998.
In return, the OFT will drop claims that their actions distorted competition and led to parents being charged higher fees than they would have paid if the information had not been circulated.
It means the schools will be less vulnerable to legal claims of compensation from angry parents.
The schools £70,000 payments will be made up of a £10,000 penalty, which must be paid straight away, and a contribution of about £60,000 to a charitable educational fund, the payment of which can be spread out over several years.
Jonathan Shephard, general secretary of the Independent Schools Council, which negotiated the settlement on behalf of the schools, said: "The settlement reached represents a sizeable cost for an inadvertent failure by the schools to recognise that the law had changed and for continuing to share information in a manner which had previously been perfectly legal.
"It does, though, enable the schools to bring an early end to a matter that has occupied them for nearly three years.
"We are pleased the OFT makes no finding that the exchange of information, a practice that ceased before the investigation began, had any effect on the level of fees."
The deal will not be confirmed until all 50 schools have signed up to it but an ISC source said the schools were expected to do so.
Vincent Smith, director of competition enforcement at the OFT, said: "The offer at this stage in the case provides an opportunity for an innovative and proportionate outcome to a case where we believe there has been a serious infringement of competition law."
Lancing College charges boarding pupils £7,295 a term, Eastbourne College charges £6,895 a term, St Leonards Mayfield School charges £6,480 a term and Worth School charges £7,055.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article