Just under half of Philadelphia's public high school graduates ever go to college.

And those who attend right after high school are more likely to succeed and to earn either two- or four-year degrees.

Those are among the findings of a report being released Thursday, based on data for more than 73,000 students who graduated from city schools from 2003 to 2009. Those numbers do not include the 29 percent of students who drop out of district schools each year.

"We need to do a better job in this city," said Lori Shorr, Mayor Nutter's chief education officer. "We only have 21 percent of our adults over the age of 25 who have a two- or four-year degree. We can't remain competitive economically that way. This data and this research is really helping us understand what is happening."

Philadelphia, she said, has a strong blue-collar tradition that was embodied in the film character Rocky Balboa. "We need to keep some of that spirit," Shorr said, "but there just aren't jobs for Rocky anymore."

One of the major goals of Nutter's administration is doubling the city's 18 percent college-attainment rate over the next five to 10 years.

The report, conducted by the OMG Center for Collaborative Learning in Center City with funding from the John S. and James L. Knight Foundation, outlines some of the challenges and college-going patterns that need to be addressed to achieve that goal.

The report calls for continuing efforts to improve students' academic preparation, providing more support and guidance for students, and building on programs that foster a culture in schools and neighborhoods in which students are expected to go to college. This is especially challenging in a district where a majority of students are low-income.

Overall, Philadelphia students lag the nation in college attendance: 37 percent of graduates immediately enrolled in college, compared with 69 percent nationally. An additional 12 percent of city graduates eventually attended college.

Among African American and Hispanic students, college attendance here is close to the national rate: 38 percent in Philadelphia vs. 40 percent nationally.

When students go to college matters, however.

Those who have delayed enrolling are more likely to attend two-year institutions, and more than 52.3 percent do not continue into the second year.

In fact, researchers said, delaying college emerged as the primary risk factor for leaving college before obtaining a degree.

In contrast, students who went to college immediately were much more likely to attend four-year colleges, remain in school, and earn degrees.

Researchers found that 52 percent of city students who enrolled at four-year colleges right after high school earned bachelor's degrees within six years.

Shorr called the impact of delayed enrollment startling.

"To me, this is a very big finding," Shorr said, "because now, there is a sense that a gap year is a good idea."

That a delay could hinder students' chances for success, she said, is information that could help counselors, those who run college-access programs, and students themselves.

"I think there is not a strong-enough push inside communities for college-going, that once you get out of high school, you no longer have those messages coming to you through the school," she said.

The summer after high school graduation, counselors and others should help students make the transition to college to counter what Jill Gurvey, a senior analyst at OMG, termed "the summer melt."

"The major message here," Gurvey said, "is that students who enroll immediately are more likely to attend four-year or private colleges, and these same students are still enrolled one year later, and they graduate within four to six years."

She acknowledged that students who are the most prepared might be more likely to attend four-year colleges right after high school.

Gurvey said the racial disparities in college success rates were stark. White and Asian students who enroll immediately after high school are more likely to earn degrees (60 percent) compared with Hispanic and African American students (38 percent.)

Those figures are comparable to national college-graduation rates of about 40 percent for minority students, she said.

The report outlines other challenges and college-going patterns that will need to be addressed to achieve it:

Only 49 percent of Philadelphia graduates ever enroll in two- or four-year colleges.

Only 4.3 percent of Philadelphia high school graduates who immediately enrolled in two-year colleges earned associate degrees in three years. Nationally, the only figure available, while not comparable, shows a better record: 9 percent of such students earn associate degrees in two years.

More than half of Philadelphia students attend three schools: Community College of Philadelphia (32.4 percent); Pennsylvania State University, including satellite campuses (10.2 percent); and Temple University (7.7 percent).

Students from magnet high schools are far more likely to go to college immediately - 70 percent compared to 28 percent from neighborhood high schools.

Asian students (88.7 percent) and white students (82.6 percent) who immediately attend college are more likely to return for a second year than African American students (71.9 percent) and Hispanic students (69.9 percent).

Although students who enroll at two-year colleges often are expected to transfer to four-year schools, researchers found the opposite was more often the case. Only 15 percent who immediately enrolled at two-year colleges, such as CCP, later transferred to four-year schools.

But 30 percent of students who transferred to CCP had begun at four-year schools.

"Students have various pathways to college completion," Gurvey said. "We acknowledge in the report, as well, that students who transfer from four-year to two-year schools are dealing with real-life struggles, financial and other preparedness barriers."

Judith Gay, vice president for academic affairs at CCP, said she had not seen the full report. But she questioned the three-year period in which researchers expected students to earn associate degrees. The number rises to 19 percent over six years, the report said.

Most CCP students, she said, attend part-time and hold jobs, and may have families, so it takes them longer to complete their schooling. In addition, Gay said, almost 70 percent of CCP students needed to take remedial courses.

"They are not reading, writing, or doing math at a college level," she said. "It does take longer because they are a little bit behind."

Meg Long, OMG project director, added: "The idea is to emphasize college completion as an expectation. If you are preparing for college completion, you can have multiple pathways for your education. But the academic preparation . . . will make you more successful."