The Higher Still programme has tried to provide flexibility and choice within a unified assessment system but problems have arisen because its principles have not been spelled out.
David Raffe and Cathy Howieson, of the Centre for Educational Sociology at Edinburgh University, reach this conclusion after 48 interviews with those involved in the programme.
They say Higher Still lacks a coherent philosophy and has been driven by "a kind of technological determinism". Its models and rationale of choice have not been well understood, let alone agreed, by those who will have to implement it.
For example, agreement about "open and broad Scottish Groups Awards has been difficult to resolve without agreed principles of flexibility and choice".
Professor Raffe and Ms Howieson state in their article in the journal Scottish Affairs that debate continues about whether the creation of a unified national system needs an explicit strategy, with clear principles and priorities in advance, or whether these should be built up gradually as the programme develops.