Comprehensive schools, which say they are not selective, are interviewing parents and children to pick well-behaved pupils who will boost their league table performance, says the study from the London School of Economics.
Most of the schools involved have opted out of local authority control and can decide their own admissions policy. They are choosing children according to a bewildering array of admissions criteria including appearance, parents' occupation, career aspirations and hobbies.
Comprehensive schools which used to be grammars are giving preference to the children and grandchildren of former pupils.
The three-year study, which was funded by the Economic and Social Research Council, involved interviews with 120 families whose children were transferring to secondary school in and around London.
It concludes that recent reforms allow a growing number of schools to decide their own admissions policies and select pupils and to admit children who do not live locally, favouring middle-class applicants.
The study found middle-class parents were no more likely than working- class parents to get their first choice of secondary school. But middle- class children were more likely to end up at schools with good exam results than their working-class counterparts.
Middle-class children who failed to get into their first choice of school often opted to travel to a high-scoring school which might be as much as 15 miles away.
By contrast, working-class children who applied unsuccessfully to a high- scoring school could not afford to travel and usually ended up at a nearby low-scoring school.
One single mother explained she could not afford the pounds 10 fare needed to send her son on the 15-mile train journey to school to join his middle- class classmates.
Ambitious working-class families who applied unsuccessfully to schools with good exam results eventually found themselves at lower-scoring schools than working-class families who had been less ambitious.
Dr Anne West, of the Centre for Educational Research at the London School of Economics, said: "At least with grammar and secondary modern schools the selection process was transparent. Now all these other factors are involved in selection, it is less clear what is going on.
"The main problems are that covert selection is likely to lead to social selection and that application forms are being used to ask for information, such as appearance, which is not part of the admissions criteria."
She said some parents were so daunted by the information requested on application forms that they were put off applying to some schools.Reuse content