Students who went to the same charter schools from middle school through grade 12 also did better on ACT college entrance exams, according to the Rand Corp. study, which focused on Chicago, the nation's third-largest school district.
Charter school students were 7 percent more likely to graduate from high school and 11 percent more likely to enroll in college; on average, their composite ACT scores were about half a point higher, the study found.
But researchers did not draw conclusions about what, if anything, the charter schools might do better than traditional public schools to achieve the higher graduation and college-enrollment rates.
"That is something we'd like to know," Brian Gill, one of the study's authors, said Wednesday. "I agree that it is a fascinating next question and we'd actually love to do some follow-up work."
Charter schools are publicly funded but usually free of many of the regulations that govern traditional public schools. There are more than 4,000 charter schools in the United States serving more than a million students, according to the study.
The study includes data from the 1997-98 through 2006-07 school years, except for graduation and college attainment data, which included 1997-98 through 2005-06. Researchers from Mathematica Policy Research, Inc. and Florida State University also participated.
The researchers plan to release similar studies on charter schools in other cities and states later this year.
Those on both sides of an ongoing debate about charter schools are likely to find fodder in the report.
Supporters can point to the graduation and college rates, while opponents can single out findings that overall test-score performance in charter schools don't differ much from scores in traditional schools.
Some critics have said charter schools might fare better because they pull the better students away from traditional public schools. But the Rand report said it found no evidence of what it called "skimming of the cream" in Chicago.
The high school students in the study had all attended charter schools in eighth grade. The comparison was between those who then went on traditional public schools and those who continued in the same charter school.
The continuity of the latter group may at least party explain their higher graduation and college-entry rates, Gill said.
"Ninth grade is a very difficult year for a lot of kids and it could be that keeping them in the same schools would help," he said. "When the eighth-grade teachers and ninth-grade teachers are part of the same school, it might be easier for them to communicate and collaborate and keep each other informed about the needs of their kids."
Jeffrey Henig, a professor of political science and education at Columbia University, said the apparent advantages of staying in the same school from middle grades through high school could be the most important finding in the new study.
"If this, in general, is the case, then both charter and non-charters might want to think about what they can do to reduce those disruptions between grades," he said.
Authors of the Rand report stressed the scope of their report was limited and they did not conclude charter schools were superior to traditional public schools.
That didn't stop charter-school proponents from heralding the findings.
"This study confirms that charter schools in Chicago are providing students with a top-notch education," said U.S. Rep. Rahm Emanuel, an Illinois Democrat.
Education officials in Chicago echoed that.
"We're very pleased to hear how well our charter school students are prepared for their future," said Arne Duncan, CEO of Chicago Public Schools.
