PORTLAND (AP) — One in five Oregon high school graduates dropped out of public universities statewide before their sophomore year in 2004, new state figures show.

Despite many who earned a B average in college prep classes, more than 1,300 graduates of Oregon high schools found themselves unprepared for the demands of college, officials said.

Most of the students who quit college were barely earning a C average, putting them at the threshold for academic probation, said Bob Kieran, director of institutional research for the Oregon University System.

Graduates of private high schools didn’t fare much better than graduates of public schools.

Statewide, 17 percent of private high school graduates who entered state universities in 2004 dropped out compared with 19 percent of public high school graduates, according to Oregon University System figures.

But the results differ dramatically among high schools.

Nine out of 10 Redmond High School graduates made it to their sophomore year in college after entering Oregon State University, the University of Oregon, Western Oregon University or another state university in fall 2004.

But nearly one out of every two graduates of Dayton High School who entered a state university in fall 2004 dropped out as freshmen, state figures show.

There also were striking differences among universities.

At the University of Oregon, with the highest admission standards among state universities, 87 percent of Oregon high school graduates who entered as freshmen in 2004 made it to their sophomore year.

But at Western Oregon and Eastern Oregon universities, nearly one of three incoming Oregon high school graduates quit before their sophomore year. And Portland State University lost 26 percent of that student group.

Educators at schools with strong track records, including Tualatin High and Beaverton’s Sunset High, say tougher high school courses help students thrive in college.

Research backs them up. A 1999 U.S. Department of Education study examined the performance of thousands of high school students, then followed them in college.

The federal study found that the academic intensity of a student’s high school course work was the top factor influencing whether students earned a college degree — more than family income, high school grades, ethnicity or test scores.

An update of that study published last week reaffirmed that taking hard classes in high school is the most crucial step toward getting a college degree.

“The bottom line is that curricular intensity counts more than grades,’’ said Clifford Adelman, author of both studies.