They did note a 'modest' gain of 1.5 percentage points at GCSE level for every £500 extra in funding per pupil.
The government says specialisms drive up standards and that success came from partnerships forged in the community.
The study looked at all state secondary schools in England between 1999 and 2004, taking in the percentage of students getting five or more good GCSEs and data on school expenditure.
It took into account a number of variables, to distinguish their effects on specialist schools from their effects on schools generally.
The only major category with a statistically significant performance differential is sports, where the effect was an estimated reduction in school performance
"This enables us to question whether school improvement is due to increased funding, specialist status, financial and institutional changes acting together, or is independent of these policy changes," says the preliminary report.
Schools must raise private sponsorship to bid for specialist status, then get at least £100,000 in capital funding, plus extra money per pupil.
The researchers found that increased finance was associated with a "modest" performance gain - so a fifth more per pupil, about £500, was needed to raise performance by 1.5 percentage points.
Previous studies have found no consistent relationship between resources and results in schools worldwide.
The effect of expenditure on specialist schools was not significantly different from the effect on schools in general - achieving "about the same" return in terms of exam performance as additional funding for state schools generally.
Specialist schools outperformed schools generally by around four percentage points - but statistically this was "not sufficiently robust to inform policy debate", the study found.
