Students in New Jersey charter schools show greater learning gains, on average, than those in comparable traditional public schools, a study released Tuesday by a Stanford University research center shows.

While the report by the Center for Research on Education Outcomes (CREDO) was positive for charters statewide, Camden's charter schools overall did not share in the good news.

The study said comparable students in the public schools from which Camden's charter students are drawn showed greater gains in reading ability on state tests than students in the charters and about the same gains in math as the city's charters. The study did not release information on individual charter performance.

Charters in the state's rural areas performed worse in both math and reading than the schools from which their students came.

New Jersey now has 86 charter schools, with more than 30,000 students; the study ended in 2011, so recently established schools were not included. Camden has more than 3,000 students in nine charters.

The report provides a first in-depth comparison of academic performance and growth between New Jersey charters and traditional public schools, CREDO said in a statement.

New Jersey Education Commissioner Chris Cerf hailed the results. CREDO's report, he said in a statement, "reflects the work we have undertaken . . . to increase our accountability standards, strengthen the rigor of our authorizing process, and, when necessary, close schools that are underperforming."

Gloria Bonilla-Santiago, chair of Camden's LEAP Academy University Charter School, said the CREDO report was important because "it highlights the debate about what charter schools bring to student performance; we are growing and doing better." Beyond just comparing test score results, she said, "what makes charters unique is the quality of teaching and the care we provide to our students."

Steve Baker, a spokesman for the New Jersey Education Association, said, "It's good news anytime students are doing well." But he added that though the CREDO study matched charter school student characteristics with those of comparable regular public school children, the schools they attend have different student makeups and that might influence student performance.

"You have to be very careful about thinking about this as an apples-to-apples comparison," he said.

CREDO director Margaret Raymond responded that the charters and the schools they come from have similar demographics in many respects.

Statewide, New Jersey charter school students in grades three to eight on average gained an additional two months of learning per year in reading and an additional three months of learning per year in math compared with their regular public school counterparts.

And 30 percent of the charter schools had significantly more positive gains in student learning than traditional public school counterparts in reading, while 11 percent of charter schools had significantly lower learning gains. In math, 40 percent of the charters outperformed their regular public school peers in learning gains; 13 percent performed worse.

The report covers the 2006-07 to 2010-11 school years. Some comparisons are for only two years: 2009-10 and 2010-11.

The results are not all good news for charters.

Though they had better achievement than comparable students in surrounding schools, 78 percent of charter students statewide still showed lower academic achievement than the state average in reading, and 35 percent showed both low reading achievement and low growth. In math, about 76 percent performed below the state average and about 26 percent showed both low achievement and low growth.

New Jersey charters did better overall than those in a 2009 CREDO study of charters in 15 states and the District of Columbia and better than Pennsylvania charters in a 2011 study by the organization.