Figures just released reveal that councils are spending up to pound;3,600 per pupil maintaining school sixth forms in the face of fierce competition from further education colleges.
The analysis by the National Association of Head Teachers shows that education authorities make, on average, annual per-capita payments of pound;2,868.
The average spent per pupil nationally in 11-16 schools is pound;2,522. In 11-18 schools it rises to pound;2,568 and in sixth forms, it jumps a further pound;300.
But schools have also been accused of downgrading post-16 education after the survey revealed that around half of all councils in England spend more on compulsory school-age education than on the post-16 sector.
It shows that 11-16 schools in Calderdale get an average pound;565 more per pupil than those with sixth forms - pound;2,945 compared with pound;2,380.
In Wolverhampton, 11 to 16-year-olds were worth an average pound;488 more and in Bristol, an extra pound;377. Both local authorities allocated more than pound;3,000 per pupil.
According to the NAHT, the London boroughs of Croydon and Camden give their 11-18 schools the most per pupil - up to pound;3,600 and pound;3,300 respectively.
But the greatest difference between 11-16 and 11-18 funding was in Bedfordshire, which allocates an average pound;735 more per pupi to schools with sixth forms.
The meanest funders for schools with sixth forms were Buckinghamshire, at an average pound;2,203, and Gloucestershire at pound;2,252.
The information, obtained from local authorities, will fuel the dispute over post-16 funding due to be handed over to the Learning and Skills Council in 2002.
The Government has already questioned why sixth-form colleges produce good results for less money and said councils are under no obligation to fund a boom in student numbers or prop up dwindling sixth forms.
David Hart, general secretary of the NAHT, said many councils had now decided that post-16 was no longer a priority.
And he said the disclosure that around half of the 150 English councils were now spending more on 11-16 education than schools with sixth forms was amazing.
"It goes against all established thinking - that the older the pupil gets the more expensive they become," said Mr Hart.
But Graham Lane, education chair of the Local Government Association, denied claims that post-16 education was now a low priority for councils. "They are as interested in post-16 as they are post-18, the over-25s and the pre-16s."
There has long been anger in the further education sector that schools are better funded than colleges. The latter have long argued for a level playing field.
On average, schools spend pound;1,500 more than colleges for each student taking three A-levels.