The Department for Education and Employment study suggests funding per student is similar in schools and colleges, while sixth-form colleges top the cost league.
Public funding for a student taking three A-levels in a school is only marginally more than for a further education counterpart, and is less than the cost of the same provision in a sixth-form college, the study says.
The figures were challenged by the Colleges' Employers' Forum, which dismissed the suggestion that comparative costs are virtually equal as "preposterous".
CEF chief executive Roger Ward said documentary evidence in the report did not support the conclusions. "We find the overall conclusions neither sound nor reliable," he said. The CEF rejects the document's conclusion that schools are not using cash from younger age groups to subsidise spending on 16 to 19 year-olds.
The DFEE figures show sixth-form colleges receive around 7 per cent more for each student gaining three A-levels than schools or FE colleges.
The picture of FE colleges as value-for-money institutions is not sustained when the report - which acknowledges its figures are subject to "significant margins of error" - turns to the cost of advanced vocational study.
Public funding of level three national vocational qualifications is found to be 60 per cent higher in colleges than training and enterprise councils. One reason for the difference is employers' contribution to the costs of training on youth training programmes.
The gap is now narrowing because of increased funding with the launch of Modern Apprenticeships and the savings made by colleges under the regime of the Further Education Funding Council.
The report also highlights significant variations within sectors themselves, particularly in schools. In colleges, the variations depended on size, location, mix of students and inherited staff costs, though class sizes and the cost and use of staff also played a part.