In an initiative aimed at reducing the number of dropouts, students will focus on up to two "areas of interest" linked to their career goals, from 2007.
The 14-year-olds will nominate a subject in which they will take four years of coursework, with the option of specialising in another one or taking a range of other courses. They can effectively "major" in vocational options, such as carpentry, as well as academic subjects.
However, all will have to continue with a compulsory core of English, maths and science.
The scheme aims to keep those at risk of dropping out motivated and engaged. Students will get guidance in choosing their "major" and can switch at any time.
More than 28 per cent of Florida pupils left school before the age of 18 in 2004-5, a typical figure across America. US students specialise later than British ones, studying a menu of optional subjects, alongside English, maths and science; and not really concentrating on any one subject until university.
Florida is now in the vanguard of a trend to steer younger students towards more specialisation. Similar initiatives are pending or in place in five states.
Sunny Deye of the National Conference of State Legislatures said: "Part of the reason states are doing this is the high number of dropouts reporting that if they'd been more interested in school they'd have stayed on."
Mark Pudlow, of Florida's teachers' union, the Florida Education Association, said allowing students to change their major eased concerns that they were too young to make such decisions, but he also warned they could forfeit exposure to a "more rounded education". The stress on core subjects has already made civics education, history and art take a back seat.