GRAMMAR schools do not undermine the performance of non-selective schools, according to a study by Parliament’s spending watchdog.

The study, conducted by the National Audit Office, also says grammars are most effective at helping 14-year-olds achieve their potential but when it comes to GCSEs, there is little difference between them and non-selective schools.

The conclusion that selective schools have no “significant effect” on other schools will disappoint anti-grammar school campaigners in Kent. They have long argued that selection adversely affects the performance of non-selective schools.

The findings appear in a report calling on the Government to take into account a wider range of data about pupils’ social background when grading schools.

It says the country’s remaining 164 grammars, 39 of which are in Kent and Medway, made a bigger difference to the academic achievements of pupils than the average for other schools at Key Stage 3.

These are the tests taken by 14-year-olds in English, maths and science each year.

The study also found grammars were particularly beneficial to pupils with a relatively lower level of prior academic achievement. However, grammars made a smaller difference when it came to GCSE results.

Cllr Paul Carter, KCC's Conservative cabinet member for education, welcomed the findings.

“It is good news. It is important to remember that secondary school results in Kent are above the national average. I have always believed that if you are to have a selective system like the one in Kent, you have to show that it is capable of adding value,” he said.

Martin Frey, of Kent campaign group STEP - Stop The Eleven Plus - said parents might just as well throw a dice as base their decisions about schools on league tables.

He added: “When prior circumstances are taken into account there appears to be very little overall difference between selective and comprehensive schooling outcomes at 16 and 18.

"The financial cost, social division and emotional stress of selection are in no way justified on any educational evidence provided by this report.”

According to the National Audit Office, many of the country’s poorest-performing schools would climb up the league tables if factors such as poverty, based on free school meals, and ethnicity were taken into account.

Selective, specialist and faith schools would still top the rankings, however.