Many small sixth forms should be closed because they are expensive and no longer meet the needs of most learners, says a new report from inspection agency Estyn.
School sixth forms offer a limited range of courses - normally around 16 A-level programmes - for the most academically able, says the report. That compares to up to 40 A-level courses available at further education colleges, which also give students more vocational options.
The agency says small sixth forms (defined as having fewer than 150 pupils by the Audit Commission) should be merged into "super" sixth forms, offering a wide range of both vocational and academic courses to learners from all educational backgrounds.
The new sixth-form centres would work with local FE colleges and offer better value for money than traditional school provision.
Only small sixth forms with outstanding results, or those with specialist, bilingual or religious provision should be protected, says Estyn. Wales has 171 sixth forms.
Education unions have reacted angrily to Estyn's proposals, saying they would disrupt schools and pupils and be unpopular with parents. The agency interviewed senior staff from schools, colleges, local education authorities and vocationally-led community consortia for education and training (CCETs) while compiling the report on post-16 school provision.
It says teaching and learning standards in school sixth forms are high, and that collaboration with FE colleges is improving. But schools are still reluctant to co-operate for fear of losing students - particularly the brightest. Practical issues, such as joint time-tabling, are also hampering efforts to broaden the options available to post-16 students.
The report acknowledges the "reluctance of many schools to accept reorganisation, or the closure of sixth-form provision". But it says LEAs and post-16 funding agency ELWa need to reorganise provision, "especially where there are small sixth forms, to improve options for learners and secure a more efficient system".
Gethin Lewis, secretary of the National Union of Teachers Cymru, said:
"This would just be a cost-cutting exercise."
Anna Brychan, director of the National Association of Head Teachers Cymru, said: "We're concerned that the learner is in danger of being lost in all of this."
Rhondda Cynon Taf and rural Powys and Carmarthenshire have the greatest number of sixth forms. But Brian Rowlands, secretary of the Secondary Heads Association Cymru, did not think small sixth forms in rural areas would be targeted: "The report appears to be a solution for small urban sixth forms."
Recent research by Cardiff university professor James Foreman-Peck found that GCSE pupils did better at schools without sixth forms (TES Cymru, June 10). But the academic said Estyn's "radical" proposals for sixth forms should be treated with caution.
He said: "I would feel happier if there was more evidence on the outcomes of what is proposed. The pay-offs per pupil can be seen as higher in smaller sixth-form groups - one teacher can spend more time with fewer pupils."
But Martin Price, chair of governors at Sir Richard Gwyn RC high school in Barry, south Wales, said that since the school's sixth form had closed, GCSE results had improved and Year 11 pupils had become role models.
The Assembly government has no plans to rationalise sixth forms.
Dr John Graystone, chief executive at fforwm, the association of colleges in Wales, said: "It is vital that learners are given an extensive choice of subjects.
"FE colleges offer a much broader range of subjects and we feel learners would benefit from further school-college collaboration."