An independent inquiry has laid bare both the callousness of policies which forced pupils out of a highly selective state school, and their downright illegality. St Olave’s, a grammar school in Orpington, south-east London, treated its students as “collateral damage”, the scathing report commissioned by Bromley council has found. The lengths to which it went to uphold and burnish its reputation for academic excellence are extraordinary and would be absurd if not so damaging to the children affected. But the case is not an anomaly; instead, it lies at the extreme end of a much more widespread problem.

The scandal emerged when the Guardian revealed that teenagers had been pushed out of the school halfway through the sixth form after failing to get top grades in end-of-year exams, leaving them distraught and struggling to find places to finish their A-levels. It was illegal to withdraw these places on academic grounds at this stage. Faced with legal action by parents and embarrassing publicity, the school reversed the policy. The headteacher was suspended and then resigned.

Wednesday’s report offers further shocking details of the school’s treatment of pupils coping with stressful circumstances including bereavement, health issues and abuse; and of how students were rejected without discussion or support. One of the peculiar aspects of the case is that St Olave’s results – as a selective school in a wealthy area – were already outstanding. High-achieving children were told they were not up to scratch. Other institutions have more basic concerns, being desperate to meet floor targets and to compete for pupils via their place in league tables. Amanda Spielman, the chief inspector of schools, has rightly highlighted the problem of “off-rolling” children to protect schools’ results, and has warned that children with special educational needs and disabilities are particularly vulnerable. Rejection is not always explicit; parents can be persuaded that their children would be better off elsewhere.

The problem is not merely that statistics fail to capture the true performance of schools. It is that measures meant to assess performance have become targets in their own right, distorting priorities. While many teachers remain dedicated to helping all students reach their potential, St Olave’s was not alone in “putting the institution above the pupils when in fact the institution is the pupils”, as the inquiry put it.

Secondly, the report testifies to an alarming lack of oversight to set things right when they go wrong – a concern also raised with regard to academies by MPs this week. The Department for Education lacks the capacity to make up for the shrinking role of local authorities. Parents complained to a succession of bodies, from the board of governors to Ofsted, without effect. Bromley council should be commended for commissioning this report; other local authorities should read it carefully. But a more fundamental reconsideration of the purpose of schools, and how we can make sure they achieve it, is needed.