When Charlotte Gregory returned to Plant High School this fall to begin her junior year, she thought she'd be taking typing and advanced-placement art. Instead, she was told she'd have to take calculus and physics.
Students in many Florida high schools are having to drop elective courses - or stay after school - in order to take tougher science and math requirements mandated by the state Legislature this summer.
The new standards are part of the bill known as ''RAISE'' - Raise Achievement In Secondary Education - designed to pull the state's education system out of mediocrity.
For the first time, the State of Florida has set graduation requirements, something local school boards have done in the past. In most cases, the state standards are higher.
The Legislature also passed a number of tax increases to cover the extra cost of the program - $233 million a year for extra teachers and other needs.
''We had two impetuses for this legislation,'' explains state Sen. Betty Castor (D) who helped write both the education and appropriation bills. ''First, we had a Florida education commission tell us that Florida's public schools were inadequate.'' Then, she says, the President's National Commission on Excellence in Education issued its report on deficiencies in the nation's schools.
Many Florida students were graduating with a minimal education, without the academic skills that educators say are needed for today's job market, she says. In some counties only two English courses were required for graduation.
Among the changes approved by the Legislature:
* The number of credits required for graduation will rise gradually from the present 20 to a total of 24 by 1987. In that year, graduating seniors will be required to have four courses in English that concentrate on literature and composition, three courses each of math and science, and at least one course each in economics, American government, American history, world history, performing arts, and life-management skills.
* All sophomores will be taking a new English course that will require weekly writing assignments. Class sizes will be limited to 20 students so that teachers will have the time to critique the writing.
* This year's sophomores will also be the first class to be required to have a 1.5 average on a scale of 4 in order to graduate, rather than just a passing average of 1.0. That same grade-point average will also be required for high-school students wishing to participate in extracurricular activities, including sports.
* Seniors will no longer be able to leave school early if they have finished their graduation requirements. Many seniors have been attending school for only a couple of hours a day and then leaving for part-time jobs. Now they will have to take classes all day, even if their graduation requirements are fulfilled.
* The state will be providing about $19 million this year for schools to buy more classroom computers and software as well as to renovate science laboratories.
* More teachers will be trained next summer in math and science to ensure that enough teachers are qualified in those subjects to meet the needs of expanded classes. The state will also provide scholarship loans to college juniors and seniors studying to be high school math and science teachers. If those students actually do become teachers, they will not be required to repay the loans.
* A study commission was established to devise a merit-pay system for teachers within a year, and extra money will be earmarked for teachers who hold master's degrees in their fields. The same commission will also be looking at ways to lengthen the school day by one period beginning next year.
Expectably, some students were less than pleased with the changes.
''Ever since junior high, they have us plan our schedule for all four years of high school,'' says 11th-grader Charlotte Gregory. ''Now they throw this on us. . . . I think it's bad they did it so fast.''
Others complain that plans for part-time jobs will have to be canceled and that they will be taking courses that they don't want.
Senator Castor concedes that the rigorous requirements could hurt marginal students. ''Some students will never be able to keep up, and we will have to monitor closely what happens to those students. It's one of the lingering doubts we have.''
But overall, she says, public reaction has been good, and the school year started this fall with minimum disruption.