The latest round of schools to be awarded specialist status, annou-nced this week, has brought the total number up to 1,686 - 54 per cent of England's secondary schools.
The 238 additions include the country's first designated specialist music college and four humanities colleges. The new category of rural schools has yet to be applied for.
Elizabeth Reid, chief executive of the Specialist Schools Trust, said: "I am delighted that the number of specialist schools has continued to grow and with the first music and humanities specialist schools, the programme has entered a new phase with a wide range of specialisms for schools to choose."
The trust is confident that nearly all schools will be specialist by 2006.
But the largest teaching unions remain sceptical.
John Bangs, head of education at the National Union of Teachers, said he was concerned that a two-tier system of funding is being constructed between those schools which have the status and those which do not.
Specialist school status provides a one-off pound;100,000 capital grant from the Government along with annual grants of pound;126 per pupil.
Chris Keates, deputy general secretary of the National Association of Schoolmasters Union of Women Teachers, said: "NASUWT'sconcerns about differential levels of funding, the ability of schools to select a percentage of pupils and the real possibility of a two-tier education system continue."
The most popular choices for specialisms this time roundwere: science (54 schools); maths and computing (37); arts (32); and sport (30).
Pupils from specialist schools significantly outperformed teen-agers from non-specialist schools in the 2003 GCSEs.
A report, published earlier this month by the Specialist Schools Trust, showed that 56 per cent of pupils from specialist schools achieved five Cs or better at GCSE in 2003. This compares to 47.1 per cent of non-specialist pupils.
However, pupils at sports colleges, which had the poorest results, gained only 48 per cent.