County offices of education are working with districts identified for "differentiated assistance" due to poor performance by student subgroups.
The study showed a significant increase in math performance, especially among low-income high school students.
The numbers vary among ethnic groups, school districts and individual high schools.
State statistics show that 83.2 percent of students who entered high school in 2012-13 had graduated by 2016. But gaps as large as 20 percentage points separate some ethnic groups.
If the suspension rate were lowered by 1 percent in one graduating class in California, the state would avoid $180 million in economic losses, researchers at the University of California have found.
California high school graduation rates are slightly below the national average but are rising more quickly.