ST. LOUIS -- Students at St. Louis charter schools, which began opening two years ago as an alternative to failing urban schools, are scoring significantly lower on state exams than pupils at St. Louis Public Schools.

Recently released test scores for the spring show charter school students scoring below the city district average in every category tested, from communication arts and social studies, to math and science, the St. Louis Post-Dispatch reported Tuesday.

But despite two consecutive years of low test scores, many are hesitant to draw conclusions about the effectiveness of the city's charter schools. Rating the schools, they say, takes more time than two years. And comparing charter schools to other public schools isn't as simple as looking at two sets of scores.

'Going to be a while'

"It's going to be a while before you can say that charter schools are working or that they aren't making a difference," said Tracye Bruno of Chancellor Beacon Academies, a company that manages three St. Louis charter schools.

Charter schools are tax-funded public schools operated by private boards. The schools are freed from many regulations in exchange for promising higher student performance.

Whether the nation's 2,400 charter schools are meeting that promise is an open question, researchers say. Several studies -- including one released last month by the Brookings Institute -- have tracked lower scores among charter school students.

But that doesn't necessarily mean the charter schools are failing. The test scores could be more of a reflection of what pupils knew before they enrolled at a charter school.

There is also some evidence that charter schools tend to attract pupils who are already behind in their studies.

Showing improvement

Doug Thaman heads the St. Louis Charter School, with 918 students. He said the majority of those enrolling at his school are at least a year behind their grade level. Those who have been with the school from the start, he said, are showing considerable improvement.

Jo Ann Perkins, principal of the Lift For Life Academy charter school, said she's tested her students using a battery of exams and she knows they are improving rapidly.

For now, she said, that's not reflected in state exams, but she predicts that scores will surge.

"We know we're on the right track," she said.

The pressure is on charter schools to produce results, since they can be closed at any time for academic failure.

They also operate under five-year charters, which must be renewed for them to stay open.

But state officials have said that charter schools cannot be fairly judged until they have produced three years of test scores. Of the seven charter schools in St. Louis, just two have taken state exams more than once.

Dave Camden, of the Missouri Charter School Information Center in Clayton, said if a school has dismal scores for three years in a row, as well as problems with its management, regulators probably ought to look at closing it.