A few years ago, bolstered by research done at the University of Chicago, Chicago Public Schools put a lot of effort into making sure its ninth graders didn’t fail core courses like math and social studies, or miss too many days of class, to help ensure students would be “on track” to graduate from high school.

Now the U. of C.’s Consortium on Chicago School Research, the same group that did the earlier analysis, is urging schools that want to make sure ninth graders go on to graduate and attend college encourage them to work hard in noncore areas, too. Specifically, in art and gym.

That’s because students’ poor performance in those subjects is behind a troubling drop in grade point averages between eighth grade and ninth grade, researchers found. The drop amounts to about a third of a letter grade for freshmen GPAs citywide.

Some of the biggest drops in grades are being seen among high-performing African-American and Latino students, especially those enrolled in elite selective enrollment high schools, according to the report, “Hidden Risk: Changes in GPA across the Transition to High School,” scheduled for release Thursday.

Researchers found that at five of the eight competitive test-in schools with at least 20 black freshmen, the average black student’s GPA declined more than two-thirds of a letter grade between the eighth and ninth grades, about double the decline of white students with similar eighth-grade GPAs.

“I think people will tend to point to, ‘Oh high school is harder,’” author Jenny Nagoaka said.

But her analysis of GPAs over six years showed something else: “A lot of it has to do with the change in the environment,” and changes such as students having to make longer commutes across town to get from their neighborhoods to a selective high school.

Results varied widely from school to school, but in general, the report concluded that “black and Latino students aren’t receiving the supports they need to make a successful transition to high school.”

Increases in freshman on-track rates correspond with a rise in graduation rates, and in calculating on-track rates, also one of the criteria that determines a high school’s rating, CPS only counts how many core classes each freshman passes or fails.

Discounting art or gym may be short-sighted, co-author Alex Seeskin said.

“Failure in non-core classes is connected just as much to high school graduation as failure during freshman year of core classes. It throws them,” he said of freshmen.

CPS CEO Janice Jackson called the connection between failing art or gym and a student’s chances of graduating “very illuminating.”

“I think high school principals definitely have to pay more attention to these courses,” she said, especially if CPS’ current on-track rate of about 89 percent is to continue to improve.

“The data shows us perhaps focusing on non-core classes in a more deep and intentional way can really get that next group of students to be successful, over that hump,” she said.

She hasn’t yet decided whether those courses should be included in calculating on-track rates.

She said she’ll discuss next month with principals and other leaders why black and Latino students appear to be struggling more than their peers while transitioning to high school, but agreed with the researchers that elementary schools need to “beef up their curriculum” so high school isn’t “so new and shocking.”

In addition to the GPA drop, the annual status report found that 19 of 100 CPS high school students who graduated in 2010 completed college within six years, up from 18 the year before. That number falls to 10 for young black men and 13 for male Latino students.