Students in nearly 50 charter schools across the city are outperforming their peers in district schools on state tests, according to a study by an education research group at Stanford University.

The report, which was done by the Center for Research on Education Outcomes, known as CREDO, uses the same methodology the group used when looking at the performance of charter schools in several states across the country.

CREDO’s study of charter schools across the country offered a mixed picture — charter schools in some states did better than local schools, while others did worse — but New York City stands out as having a particularly successful crop of charter schools.

Overall, the study found that charter schools are scoring about five scale score points higher in math and two points higher in reading than students in district schools. It also found that in students’ first year at a charter school, their reading scores decrease modestly, but then rebound and eventually top those of district school students in the following years.

CREDO director Margaret Raymond said charter schools may be having a harder time getting their reading scores far beyond district schools’ scores because the city has been focusing on literacy programs for years.

Columbia Teachers College Professor Aaron Pallas had another theory: “The kinds of math skills that are tested are just more responsive to test prep than reading is.”

The study also found that black and Hispanic students have higher test scores than peers in district schools, but students who are not fluent in English and special education students in charter schools are not performing any differently than those in district schools.

CREDO’s study “doesn’t tell us what would happen if there was a great deal of expansion of charter schools,” Pallas said. “The new schools coming on line may not be like the ones that are already there. We don’t know much about the newer charter schools and how they’re doing.”

Published Wednesday, Jan. 20, 2010