Students who attend charter high schools are substantially more likely to graduate and go on to college than students who attend traditional public schools, a new study of Chicago schools found.

The study, the latest segment in a nationwide examination of charter schools by a nonprofit policy group, the RAND Corporation, is one of the brighter pictures of charter schools that researchers have yet provided.

Previous studies have delivered little confirmation of advocates’ position that charter schools — privately operated public schools that enjoy freedom in exchange for a promise to meet certain achievement goals or be shut down — produce, as a group, stronger results than traditional public schools.

The RAND study found that, in elementary school and middle school, students in charter schools do no better than students in traditional public schools.

But, looking to two measures never before examined in such a study, the researchers did find substantial benefits of attending charter high schools that include elementary and middle grades.

Comparing eighth-graders who left their charter school to go to a district-run high school to eighth-graders who continued at a charter school, the researchers found that the likelihood of graduating high school went up 7 percentage points for charter students, and the likelihood of entering college went up 11 percentage points.

The study also examined the criticism that charters select brighter and more involved students, or “cream-skim.” The study found scant evidence of such a practice in Chicago. Rather, students who transferred to charter schools generally were similar to the average district student, though researchers found that black and Hispanic students who moved to charters tended to be slightly more adept at reading.

What researchers said is not clear is whether being a charter school was the crucial difference — or the fact that every charter school studied includes not just high school grades but also middle and in some cases elementary school grades.

The chief executive officer of the New York City Center for Charter School Excellence, James Merriman, said the study is good news for New York City, where several charter schools are moving to expand their middle schools into high schools, as well.

Asked about the study, the president of the city teachers union, Randi Weingarten, said: “It’s probably far more productive to learn from differences between high-performing and low-performing schools. Otherwise, we’re merely falling into old stereotypes about charter versus public schools, setting up a hollow competition that pits teachers against teachers and students against each other — and everyone will lose out.”