Sir Ken Jackson, the union's general secretary, denied claims from the two largest teaching associations that by becoming the first union to invest directly in schools he was contributing to a privatised, two-tier education system.
He said: "Having specialist schools just allows them to gain expertise in a particular area. Part of being a specialist school is to work with others locally and form networks that benefit everyone.
"It's been clear that for years we haven't been delivering the skills that children need and we decided that we'd do something about it."
Schools that raise the pound;50,000 sponsorship from a business or voluntary organisation and achieve specialist status receive a pound;100,000 grant from the Department for Education and Skills and a further pound;123 per pupil for four years.