Funding for school sixth formers has fallen by more than a fifth in the past eight years amid declining investment in post-16 education, according to an authoritative study.

The Institute for Fiscal Studies (IFS) report said funding for sixth form and further education (FE) students has been been cut “much more sharply” than any other area of education, with spending per sixth form student down 21% since its peak in 2010.

FE has also been hard hit, with an 8% cut in real terms since 2010/11 – and from a lower base than sixth forms – resulting in course closures, job losses and cuts to student support services. There are also concerns about the capacity of the FE system to deliver government reforms in the absence of additional funding.

A campaign by parents and teachers to highlight the damaging impact of budget cuts has focused primarily on primary and secondary schools, but the IFS report said sixth form and FE education has been worst hit by the education budget squeeze.

Geoff Barton, the general secretary of the Association of School and College Leaders, said: “Parents will be horrified to learn of the damage that has been done to sixth forms and colleges by severe real-terms cuts in government funding. They may also wonder why the basic rate of funding for each of these students is just £4,000 compared to tuition fees at university, which can be as high as £9,250.”

He added: “There is no rhyme or reason for the extremely low level of funding for 16 to 18-year-olds, and without the additional investment that is desperately needed more courses and student support services will have to be cut in addition to those which have already been lost.”

The IFS’s inaugural annual report on education spending in England showed major changes in funding patterns at different stages in a pupil’s education. While school funding in England has fallen by 8% in real terms since 2010 – following increases of more than 50% over the 2000s – spending on early education has risen to £3bn from almost nothing in the early 1990s. Higher education funding has also risen by nearly 60% since 1997.

“In this context, the almost complete lack of growth in spending on further education is all the more remarkable,” said the report’s author and IFS research fellow, Luke Sibieta.

Sally Hunt, the general secretary of the University and College Union, said: “Severe cuts to further education funding have led to job losses, course closures and fewer learning opportunities. Staff have seen their pay fall by 25% since 2009, and many colleges are struggling to recruit the expert staff they need. The situation is completely unsustainable.”

A Department for Education spokesperson conceded that some FE colleges were working to very tight margins and had raised concerns about the impact on pastoral care, teacher recruitment and retention and workload.

The spokesperson said: “Whilst we accept that there are pressures across the system, we have protected base rate funding for 16 to 19-year-olds until 2020, and are putting more money into our schools than ever before.”

