Student group // Suspension rate

White females: 2.2 percent

Black females: 11 percent

White males: 6.2 percent

Black males: 20 percent

Student group // Expulsion rate

White females: 0.1 percent

Black females: 0.1 percent

White males: 0.2 percent

Black males: 0.4 percent

Source: Tennessee Department of Education

Black girls in Hamilton County are suspended from school at five times the rate of white girls -- a pace that lines up with a new national study that found black girls face harsher discipline than their white peers.

The study by the Columbia Law School's Center for Intersectionality and Social Policy Studies also found that race may play more of a role in the discipline of girls than boys. The researchers hope to broaden the conversation about racial bias in schools from focusing almost exclusively on black boys to also recognizing the risk for black girls.

Nationally, black girls are suspended six times more than white girls, according to the study, while black boys are suspended three times more than white boys.

The numbers are similar in Hamilton County. Here, 20 percent of all black boys were suspended during the 2013-14 school year, compared to 6.2 percent of white boys -- meaning black boys are suspended at more than three times the rate of white boys.

And 11 percent of black girls were suspended in that same school year, compared to just 2.2 percent of white girls -- meaning black girls are suspended at five times the rate of white girls.

"Because black boys are disciplined in greater numbers than any other group, a lot of people infer that black girls aren't impacted," said Rachel Gilmer, associate director of the African American Policy Forum, which co-authored the study. "But we found that black girls actually face a greater risk."

The study's authors think racial bias is to blame for the gap in numbers. But local educators aren't so sure. Lee McDade, assistant superintendent of the Hamilton County Department of Education, said the circumstances of each suspension are unique.

"I don't care if they're purple, if they are disrupting class and the teacher can't teach and the kids can't learn, then we need to deal with them," he said. "To say I lumped one ethnicity or race in together is just not the case."

But Luke Harris, program director at the African American Policy Institute, said the gap in the numbers is too wide to be explained away and biases can influence all decisions, whether or not the decision-maker recognizes the bias.

"The whole social-psychological phenomenon of implicit bias is [that] people don't realize they're acting on it," he said. "It's something that is acted on not just by whites but by people of color as well. You have to dig deeper."

The study suggests that cultural differences may exacerbate racial stereotypes: Black girls interviewed by the researchers said they felt like teachers thought they were "loud" and "ghetto."

But other teachers said girls have been more likely to get into fights than boys in recent years. Girls tend to carry disputes from social media into the classroom, said Buddy Sullivan, who teaches at East Hamilton Middle/High School. On Tuesday, eight girls got into a fight at Brainerd High School that had to be broken up by law enforcement, according to the Hamilton County Sheriff's Office.

All eight were arrested and charged with disorderly conduct -- a move condemned by the Chattanooga-Hamilton County National Association for the Advancement of Colored People, which called for an overhaul of school discipline methods.

"The disparity levels and disproportionate rates experienced by African American and minority students in terms of suspensions, expulsions, reassignment to alternative schools and other disciplinary infractions [are] funneling our students out of the schoolhouse and into the jailhouse," wrote President Elenora Woods.

But Sullivan said that the schools where he worked were slow to suspend and relied more heavily on peer-to-peer mediation and prevention than suspensions.

Marsha Drake, director of student services at Hamilton County Department of Education, said she held all students to the same standards during her eight years as a principal at Lakeside Elementary.

"The standards were the same for all," she said. "And if you were disruptive to the classroom environment, everybody got the same consequences."

Students can be suspended for various offenses, depending on the school. Fighting, gang activity, robbery, threats, trespassing, bullying, vandalism or sexual offenses are typical offenses that can result in suspension, Drake said.

The student population in Hamilton County Schools is about 57 percent white and 31 percent black. Yet black students account for 63 percent of all the suspensions handed out so far in the 2014-2015 school year, according to the Hamilton County Department of Education.

When that's broken down by gender, black girls have received 70 percent of all suspensions given to female students this school year, while black boys have received 60 percent of suspensions given to males.

The administrator has some leeway when deciding whether to suspend, depending on the circumstances of each case. Some of that prerogative carries over when a student faces expulsion, except when the student has committed a zero-tolerance offense -- bringing a firearm to school, having drugs, making threats or hitting a school employee -- that requires automatic expulsion, Drake said.

The breakdown of expelled students in Hamilton County so far this year is much more evenly divided between black and white students. Twelve black girls have been expelled while 18 white girls have been expelled. Thirty-nine black boys and 38 white boys have been expelled.

Harris said the study was intended to spark a conversation about the numbers and the differences between white and black students, but that more research is needed to understand exactly what factors are driving the disparity and how to rectify it.

In the meantime, he said, teachers and administrators should start by recognizing that there is a difference.

"The first thing they can do is to pay attention to the fact that the numbers are so dramatically different, and then try to be deeply, deeply introspective about it," Harris said.

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