JACKSONVILLE, Fla. -- Florida's public high schools have some of the worst student retention rates in the country, with half qualifying as "Dropout Factories," four times the national average, according to a new analysis of U.S. Education Department data.

The state's percentage of dropout factories, 51.1 percent, was the second-highest in the nation, slightly less than South Carolina's, according to the analysis conducted by Johns Hopkins University for The Associated Press.

The term dropout factory, coined by Hopkins researcher Bob Balfanz, describes schools where no more than 60 percent of the students who start as freshmen make it to their senior year.

Balfanz says he has a hypothesis about why Florida's numbers are so high: large schools and a focus on test scores. Schools with an average of 2,000 or 3,000 students are fairly common throughout the state, Balfanz said.

"That's an easy place for kids to be anonymous. That's a key driver of kids dropping out," Balfanz said.

In addition, the state's accountability is focused on test scores, he said. That includes passing the Florida Comprehensive Assessment Test (FCAT) to earn a diploma. With the emphasis on test scores instead of graduation rates, schools aren't heavily penalized for low retention rates, Balfanz said.

Nearly half of Florida's 67 counties have at least one dropout factory, and there are more than 150 statewide. That list includes St. Petersburg High School in Pinellas County, Gov. Charlie Crist's alma matter. Crist's office did not return a telephone call seeking comment.

Mark Pudlow, a spokesman for the Florida Education Association, agreed that the focus on test scores in Florida has had a huge affect on students. And he said he wasn't particularly surprised by the data.

"We haven't made as great an investment in education as some other states have," said Pudlow, the union that represents 136,000 teachers and school support staff statewide.

Nationwide, researchers found there are 1,700 regular or vocational high schools that can be labeled dropout factories. That's 12 percent of all such schools, about the same level as a decade ago. Utah was the only state without a dropout factory, according to the analysis, which was released Monday. In contrast, in Florida's rate only beat South Carolina's 51.9 percent rating.

Researchers used data from senior classes for three years in a row to make sure local events like plant closures aren't to blame for the low retention rates. In addition, schools with fewer than 100 students were not looked at nor were special education schools or schools where there was not three years worth of data. In Florida, the data encompassed approximately 75 percent of the population of regular and vocational schools.

Florida Department of Education spokesman Tom Butler said in an e-mail that the department uses various strategies to keep kids in school. Those include reading and mathematics courses for students who score low on the FCAT and mentoring and leadership programs, Butler said.

According to the Florida Department of Education's own calculations, 3.5 percent of Florida's students dropped out in 2005-2006. And, the dropout rate has increased slightly in the past two years despite steadily decreasing from 1998-1999 to 2003-2004, according to the department.

Justin Shin, a graduate of one of the schools labeled a dropout factory, King Senior High School in Hillsborough County, said while he was there there'd be assemblies where speakers who would "basically explain to you why you should stay in high school." Shin, who was part of a magnet program at the school, is now a freshman at Duke. He said some speakers were more effective than others.

"They talked about how much money you make as a professional versus not having a high school diploma," Shin said. "They just kind of talked about is this what you want to do with your life?"