Although more than 90 percent of the nation’s ninth graders expect to graduate from college, a report released Monday estimates that only 30 percent of California’s high school freshmen will actually earn a bachelor’s degree.

Amid that dismaying projection, researchers at the Public Policy Institute of California also unearthed a surprising finding. It’s not just lack of academic progress that’s keeping students from earning a degree. It’s also students’ failure to take the right preparatory courses and schools tracking them into remedial classes. California’s comparatively lax high-school graduation requirements may also be a contributing factor.

The numbers matter because other research estimates that by 2030 California will fall 1.1 million short of educated workers needed to keep its economy going.

In high school, “we find a significant number of students on the pathway simply stall out,” the report reads. That applies not only to struggling students, but also to high-achievers.

The report, “Improving College Pathways in California,” also pinpointed the spots where students veer from the college and graduation track.

The report analyzed data from 24 California school districts, covering more than 140,000 high school graduates from the classes of 2007 to 2014. That represented about 5 percent of the state’s high school graduates.

It recommended school districts increase the number of college-preparatory courses, place more students in those courses and beef up their graduation requirements. The report also suggested community colleges improve counseling and course placement systems, and that the state expand the capacity of its universities.

In the sample, only 38 percent of high school graduates took all the courses required for admission to a California public university. Surprisingly, the subject they’re most often lacking is English, followed closely by math.

In part, the researchers found, that’s because not all California high schools offer a complete menu of the courses required for admission to the state’s public universities: 14 percent lack appropriate English or science courses, 12 percent lack math courses and 10 percent lack social-science courses.

In addition, even some high school students who do well in a course don’t sign up for the next level.

Those detours off the college track most often happen in the junior and senior years in high school, and first two years of community college, the study found.

“The finding that even academically prepared students do not make it to or through college is very unexpected and surprising,” said Niu Gao, one of the report’s authors, along with Hans Johnson. In high school, one-third of students who earned an A or B in Algebra 1 didn’t advance to geometry, the next course. And in community college, only about 20 percent of well-prepared students were directed to at least one remedial course, the report found.

The researchers found that poor academic preparation doesn’t fully explain the disparities among different student groups, and they suggested that course placement and academic counseling might be responsible.

“Students, particularly underrepresented students, often attend schools that do not have a strong college-going history,” the report read, suggesting that students may not get appropriate information.

Gao noted California lags in high school graduation requirements. It is one of three states requiring just two years of math and one of two states requiring only three years of English.

Researchers also suggested that one of the causes for low transfer rates from community colleges was misplacement of students into remedial classes. Nearly one-third of students who had completed the required college-prep classes in high school nevertheless were placed into catch-up courses in college.

Addressing that problem could increase community college transfers by 28 percent, and produce 16 percent more graduates with bachelor degrees, the PPIC researchers estimated.

However, they also noted that California’s limited enrollment capacity at its public universities poses a major impediment to students who qualify for college. A recent study found that 40 percent of state high school graduates are eligible for CSU, higher than in previous years and higher than the state’s Higher Education Master Plan goal of 33 percent. CSU has been turning away about 19,000 freshmen annually, the report noted.