The funding of colleges and schools to provide skills programmes for secondary pupils is "complex and opaque", HMIE claims.
Its latest report on these partnerships, a key plank of the Government's flagship policy to broaden vocational education for all pupils, reveals that almost pound;4 million went unspent last year.
The number of enrolments on school-college programmes increased by 22 per cent to 51,000 between 2005 and 2007, and the Government set aside pound;37.4 million last year. But college activity, mainly for S3-4 pupils, accounted for only pound;33.5 million.
The inspectors' report said the reasons were complex, but it noted that colleges tended to over-estimate the costs of school-college programmes, citing the expense of running smaller class sizes, additional staffing and higher-than-average wastage of materials.
A plethora of funding sources gives rise to the complexity, and the report says not all colleges and education authorities understand the arrangements. Direct support comes from the Scottish Funding Council, the local authorities and school budgets, but there is also money from the European Social Fund, industry organisations, the Determined to Succeed initiative and the Schools of Ambition programme.
The SFC is reviewing these anomalies and intends to report later this year. The need for "fully clarifying" the funding issues was endorsed by Graham Donaldson, senior chief inspector of education.
Despite Pounds 4 million going a-begging, inspectors reported "considerable unmet demand" from pupils and parents. There was particular pressure on colleges in some parts of the country and in some subjects. While "most" schools and colleges (HMIE-speak for between 75 per cent and 90 per cent) are said to be enthusiastic about working together, the report adds, "the capacity of colleges to deliver many more school-college programmes in the future, and even the desirability of this approach, are currently the subject of debate".
Nonetheless, inspectors continued, "most learners have a very positive experience of school-college programmes (and) many previously disaffected learners have re-engaged with learning through (their) involvement".
Mr Donaldson reinforced the positive note, but he also called for better communication between schools and colleges about pupils' needs, more joint approaches to learning and teaching, and improved timetabling, so that more pupils could take part.
The inspection found that schools were getting better at selecting pupils who would benefit from studying at college. But there was still a tendency to encourage applications from less able pupils, especially in schools "with a more academic tradition". Some even restricted college courses to pupils intending to leave after S4.
The HMIE report continues: "Some parents were also concerned that involvement with school-college programmes would adversely affect their academic progress and discouraged uptake. When the workload of school subjects increased, particularly at examination times, some learners gave up their college programmes to concentrate on school work.
"Very widely, parents, carers and even pupils did not accord college vocational options parity of esteem with academic subjects."
The findings also point to varied experiences of programmes, depending on whether they are delivered in colleges or in schools. Most pupils appeared to like college freedom and more abundant resources. "The kit is amazing - much more up-to-date than in school," one said. Another remarked that pupils were treated with respect: "If you do something wrong, you are told how to do it right and not told it's you that's at fault."
On the other hand, some learners found college life "daunting" and "went missing". A few felt FE lecturers were too "laid back" and did not always give clear instructions.
There is a considerable difference between education authorities in the number of pupils given the opportunity to expand their vocational horizons. Fife is top of the table, with 39 per cent of its secondary pupils enrolling on college programmes. By contrast, Argyll and Bute and Falkirk have just seven per cent. The Scottish average is 16 per cent.