When Gov. Jeb Bush initiated the nation's boldest voucher experiment last year, it was clear that its fate would depend on two things: the progress of the students using taxpayer money for private-school tuition and the impact on the struggling schools they left behind.

In their Roman Catholic school plaids and pleats, the voucher children stand as symbols of the program's promise: One fourth-grade boy has finally learned to read and a third grader is mastering cursive writing; their parents consider the vouchers a blessing.

But in the debate roiling American cities over whether vouchers are the greatest threat to public schools or the best hope to solve the problems that plague them, the more vexing issues arise at two elementary schools here in an impoverished corner of the Florida Panhandle.

Florida is the first state to grant vouchers to students whose schools fail standardized tests and it will probably soon have the nation's largest voucher program. It is the model for a national program proposed by Gov. George W. Bush of Texas, the likely Republican presidential nominee.

The two schools here, A. A. Dixon and Spencer Bibbs, were the first in the state to lose students to vouchers when the law took effect last summer because so many of their pupils performed so poorly on the tests two years running. While it may take years to gauge the program's success, its impact is already apparent at the two schools, nestled in two of the state's poorest neighborhoods.

With grants from the district and the state, the schools have hired more teachers, reduced class size, stretched the school year by 30 days and added afternoon tutoring.

They have also shriveled the curriculum, emphasizing subjects that will help improve test scores, while shunning science and social studies -- subjects not covered by the tests. They are drilling children on reading, writing, math and, inevitably, test-taking tips. Field trips have disappeared, replaced by events like a recent Saturday ''test-taking fair.''

''We're leaving out important parts of the education process,'' lamented Dixon's principal, Judith O. Ladner. ''They're going to learn what's on a test. But are they going to learn to be able to cooperate with each other in the business world? Are they going to be creative thinkers?''

At its core, the question over vouchers is whether a market-based approach, embraced in so many sectors today, is appropriate for education. The notion of rating schools based on the standardized test scores of students is sweeping the nation as nearly every state strives to hold teachers and principals more accountable. But beyond providing an escape for children trapped in failing schools, vouchers may be shifting the student-teacher relationship in ways that some find troubling.

''When a low-performing child walks into a classroom,'' said Jim May, superintendent here in Escambia County, ''instead of being seen as a challenge, or an opportunity for improvement, for the first time since I've been in education, teachers are seeing them as a liability.''

First proposed by the economist Milton Friedman in 1955, vouchers have exploded from a pilot program of 300 students in Milwaukee in 1990 to 63,840 children in 31 states today, most from low-income families. That includes 11,538 students, mainly in Cleveland and Milwaukee, using public money to attend private schools, and about 70 small programs around the country that are less controversial because they are financed by philanthropists.

Florida has only 53 students using vouchers for private schools and another 85 who transferred to higher-performing public ones.

But school grades being released in June could expand the program to as many as 60,000 students in 78 schools. Those schools received ''F's'' last year because of poor performances on the Florida Comprehensive Assessment Tests and students would be eligible for vouchers if they are rated ''F'' a second time.

Though they touch only a fraction of the nation's 52 million schoolchildren, vouchers are among the most contentious issues today in cities including New York, and form a point of dissension between Mr. Bush of Texas and Vice President Al Gore, his expected Democratic opponent.

More than 25 state legislatures are considering voucher plans -- many, like Florida's, linked to standardized test performance -- while constitutional challenges to programs here and in Cleveland are expected to land before the United States Supreme Court.

The philosophical gap is wide: Opponents fear vouchers would drain resources from troubled schools, leaving them worse off for the students who stay. Advocates say that vouchers give poor children opportunities akin to the affluent and would force weak schools to improve.

Research so far has been murky, as partisans pick apart each others' studies.

Over all, experts believe that students using vouchers to attend private schools score slightly higher on math and reading tests than the students who remain in public schools.

But ''the great question that nobody can really answer,'' said John F. Witte, a University of Wisconsin political scientist who has published a book on the Milwaukee voucher program, is, ''Does it create competition and does it create change?''

Things are certainly different this year at Bibbs and Dixon, schools where nearly all the students are black and poor enough to qualify for free breakfast and lunch programs.