Money and intake made the most difference to results, researchers said
The success of England's specialist schools is an illusion, with the extra money they receive and intake being the crucial factors, according to a report.
A University of Buckingham report said the system had led to schools with names that "did not mean very much".
It said 2007 research suggested pupils at schools specialising in music were more likely to get A grades in physics A-level than those at science schools.
The government said specialist schools were "thriving" and raising standards.
And the Specialist Schools and Academies Trust said specialisms were catalysts which could improve a whole school.
Nearly all - about 90% - of secondary schools in England now specialise in a particular area of the curriculum, such as technology, languages, science, sport or the performing arts.
Such status attracts extra money from the government, but schools are required to raise up to £50,000 from the private sector to qualify.
The authors of the latest study say specialist schools appear to do better because poorer performing schools were not granted specialist status.
Professor Alan Smithers said: "All the SSAT's (Specialist Schools and Academies Trust) comparisons amount to is that if you take effective schools and give them extra money, they do better than less effective schools without extra money."
The study showed, he said, that the extra money pumped into specialist schools, as well as their intake of pupils, had the biggest impact on results.
It looked in detail at the impact of specialist science schools on physics.
There has been a dramatic slump in the numbers of students taking A-level physics and going on to study it at university since 1990.
The researchers compared the physics A-level results of the various types of specialist schools.
They found that in 2007, 23.7% of entries for physics A-level at a non-selective specialist science school or college achieved an A grade.
At specialist music schools, the rate of A grades in physics was 36% - although the total number of science schools considered (124) was far greater than that of music schools (seven).
At language specialist schools, 26.5% of entries in physics were awarded A grades at A-level (32 schools considered).
The proportion of physics A grades achieved at science specialist schools was similar to that achieved at schools specialising in maths and computing (24.4%), where 85 schools were considered, and higher than at schools specialising in the humanities, the performing arts, business and others.
Report co-author Dr Pamela Robinson said: "It could be argued that specialist schools were a useful way of freshening up 'bog standard' comprehensives.
"But it seems to have left us with a lot of schools with names that do not mean very much. It is odd having music and languages schools that do better in science than the science schools."
The SSAT said science colleges had boosted science teaching and been a catalyst for improving whole schools.
Chief executive Elizabeth Reid said: "Specialist science colleges have boosted science teaching and take-up as even Professor Smithers acknowledges.
"His report says that 70% of specialist science colleges provided GCSE physics in 2007, up from 43% in 2003 and that science colleges were over five times more likely to offer physics than other schools.
"Specialist schools are fully comprehensive and, as Professor David Jesson's annual study for the SSAT shows, use their specialism as a catalyst for whole school improvement, ensuring more young people leave school with a good education and with a good set of qualifications."
The report from the University of Buckingham concludes: "It is an urgent problem for government to find ways of bringing together what is now a diverse collection of schools into a secondary education system with shape and coherence."
A spokesman for the Department for Children, Schools and Families said: "Yet again Professor Smithers is striving to do down the hard work of teachers and pupils rather than celebrating their achievements.
"Specialist schools are thriving. Specialist status gives a valuable cash boost to schools but more importantly it gives an extra focus and drive that raises standards across the board, not just in the relevant specialism. This can only be a good thing."