We don’t want misbehaving students to stop the rest of their class from learning. But we also don’t want to suspend or expel unruly kids too quickly and risk putting them in the “school-to-prison pipeline.”

This issue is really sensitive when race is involved – the focus of an extensive new study on out-of-school suspensions in California.

Previous federal and state reports pointing out that black students get sent home much more frequently prompted the Legislature to act. Assembly Bill 420 bans students in first through third grade from being suspended from school and students in K-12 from being expelled for “willful defiance” – a catch-all category that critics say is too vague and allows racial bias to creep in. Under that broad definition, districts have suspended students for not following directions, failing to bring books to class, wearing a cap and talking back.

Even before the law took effect in January 2015, the state Department of Education and several large school districts had been trying to reduce suspensions, offering alternatives such as “restorative justice” peer courts where students, parents and teachers talk out disputes.

The department said out-of-school suspensions had dropped substantially from 2013 to 2015, with the biggest declines under “willful defiance.” Suspensions declined by about 30 percent for all racial groups of students – Asian, blacks, whites and Hispanics.

But black students were still suspended at far higher rates – 178 suspensions for every 1,000 students, compared to 52 per 1,000 for Hispanics, 44 for whites and 12 for Asians.

The Brown Center on Education Policy at the Brookings Institution takes a deeper dive into the state’s numbers to look at that difference between schools with higher suspension rates and those with lower rates. The 1,930 high-rate schools suspended more than 35,000 black students in 2015, while the 3,546 low-rate schools suspended a total of only 139, and the vast majority didn’t suspend any.

The study’s authors are right – that disparity is shocking.

Schools with higher suspension rates tend to be middle schools, larger campuses, those with more students who qualify for free or reduced-price lunches and those with higher percentages of black students. The study’s authors say that black students start feeling disciplined unfairly in middle school, that larger schools are tougher to manage, that students from poor families face more challenges, and that schools with big populations of black students may be located in unsafe neighborhoods with tougher disciplinary rules.

Once more recent suspension numbers come out, it may become clearer if the state law is working. If legislators want to keep or expand it, they have to act before it expires on July 1, 2018.

If the law isn’t making a difference, the possible underlying reasons for suspensions from the study will be far more difficult to fix.