And comprehensives prepare sixth-formers for A-levels just as effectively as selective schools, an analysis of English exam data has found. Pupils with the same GCSE results will get roughly the same A-level results whether they attend a selective or comprehensive sixth form.
However, sixth-form college students make more progress and get higher A-level grades than all other state school pupils with the same GCSEs, according to the study presented at the British Educational Research Association.
Female sixth-form college students enjoy a one-grade advantage - per person rather than per subject - over other state-educated candidates. For young men the gain amounts to around three-quarters of a grade.
Sixth-form colleges were just as good as private schools at boosting the performance of pupils with average or above-GCSE results. But pupils with poor GCSE grades make the most progress at private-school sixth forms, the study, by Min Yang and Geoffrey Woodhouse of London University's Institute of Education, concluded. They analysed exam data for nearly 723,000 students from 1994 to 1997.
The "vaue" that an individual school or college adds in the sixth form was found to depend on the average GCSE results its pupils achieved lower down the school. Schools which scored high average GCSE results widened the performance gap between themselves and lower performing but otherwise similar schools.
Students with the best GCSE results in each school made the most progress, the study found.
Ms Min Yang said: "Once these effects were taken into account the differences in student progress between comprehensives and grammars cease to be detectable."
Students in the north of England tended to score less highly at A-level than students in the rest of England with similar GCSEs.
Girls with good GCSE grades (C or above) study fewer subjects than similarly qualified boys in the sixth form. Girls entered fewer AAS levels and got lower overall scores than boys with similar GCSE grades, the study found.
Older students make less progress than their younger classmates with similar GCSEs.
Earlier this year a study, by Professor David Jesson of York University, concluded that grammars produce less improvement than comprehensives in the two years before GCSE.
Research conference reports: 6, 28, 29, 33 and 36