The government has been "complicit" in an illegal policy that saw a school force out pupils unlikely to achieve high grades, campaigners have claimed. They said the Department for Education did not take punitive steps against the head at St Olave's school in south-east London because it was partly to blame.
The DfE's increasingly stringent league table criteria forces schools into "dubious" policies, campaigners said.
The DfE said it wrote to schools to say such expulsions were illegal last year.
The practice, found to be illegal in an independent inquiry commissioned by Bromley Council, was introduced and overseen at the school in Orpington over a seven year-period by former headmaster Aydin Önaç. It was reversed in September when a group of parents threatened a judicial review and Mr Önaç resigned at the end of 2017.
According to the BBC Mr Önaç has been referred to regulatory body the Teaching Regulation Agency (TRA), but Andrew Gebbett, who has two sons at St Olave's, said he believed the DfE should have "taken the lead”.
The DfE said it wrote to secondary schools reminding them the policy was unlawful.
Education law specialist Anita Chopra said it was usual for such referrals to be made by an employer or a parent. She said if the TRA decided Mr Önaç's case was worth investigating, he could be banned from teaching.
Nuala Burgess, spokeswoman for campaign group Comprehensive Future, said she believed the DfE was complicit by "indirectly forcing schools to do these things”.
DfE policies placing increasing importance on league tables drove schools into "all sorts of dubious practices, including the 'weeding out' of year 12s," said Ms Burgess, who recently completed a doctorate into sixth form selective practices.