In March the U.S. Department of Education released the Civil Rights Data Collection, a self-reported survey of more than 72,000 schools that serve 85 percent of American students. Among the tool's findings is that African-American and Latino students receive harsher school discipline than their white counterparts. Black students are more than three times as likely, for example, to be suspended or expelled, and one in five African-American boys received an out-of-school suspension.

Department of Education officials stressed that the data alone, which don't provide details behind the numbers, do not verify discrimination or violations of civil rights law. "But CRDC's most useful function may ultimately be in its potential to serve as a mirror," wrote Russlynn Ali, the Education Department's assistant secretary for civil rights, in a CNN op-ed.

Several weeks after the report came out, new details emerged about Trayvon Martin, an unarmed African-American teen shot and killed in February by George Zimmerman. Trayvon, 17, was from Miami but visiting his father in Sanford, Fla., at the time of his death. As reported by  the Miami Herald, he was in Sanford while serving a 10-day suspension from school.

The offense for the punishment: getting caught with a plastic bag containing traces of marijuana. Under the Miami-Dade County school district's zero-tolerance policy for drug possession, it was enough to warrant the lengthy out-of-school suspension. The Herald also reported that Trayvon had served two previous out-of-school suspensions, one for truancy and the other for graffiti after a security camera caught him scrawling "WTF" on a locker.

According to Russell Skiba, one contributor to such racial disparities around school suspensions has been the rise of zero-tolerance discipline policies. "A whole range of more punitive policies are put in place in schools with more minority students," said Skiba, director of Indiana University Bloomington's Equity Project, a research consortium that provides information to educators and policymakers on equity in school discipline. "It doesn't matter whether it's a rich school, poor school, urban school or suburban school. Where there are more black and Latino students, there is a higher likelihood of policies of zero tolerance, out-of-school suspensions and expulsions."

Trayvon Martin's school district reflects this pattern. According to CRDC, Miami-Dade County public school students are 64.5 percent Hispanic, 25.2 percent black, 8.9 percent white and 1.3 percent Asian.

Daniel Losen, director of UCLA's Center for Civil Rights Remedies, said that the frequent use of out-of-school suspension began taking root in the 1970s. "There's always been an undercurrent of educators who suggest that we have to 'get tough' on kids," said Losen, citing the example of former Eastside High School principal Joe Clark patrolling hallways with a bat and a bullhorn, as immortalized in the 1989 biographical film Lean on Me.

While Losen suggested that the "get tough" trend is sometimes fueled by stereotypes and biases against minority students, he also said that it can be motivated by well-meaning administrators who feel that strict enforcement over everything is the best policy.

"But it's fundamentally unsound educational policy to kick kids out of school for minor infractions," he said, adding that most suspensions are not for the most dangerous or violent offenses but for things like truancy, dress code violations and subjective behaviors like disrespect and loitering. "There's no research to support that out-of-school suspension is going to help improve a student's behavior. To the contrary, with no guarantee of adult supervision, educators may be reinforcing the exact behavior they think they're correcting."

Moreover, said Losen, a record of school suspension is irrelevant to Trayvon Martin's shooting. "There's been a lot of press that seems to be implying that he was not worth much just because he had been suspended from school for marijuana residue, or that the shooter was justified because this kid may have smoked pot," he said. "The idea that his life is less valuable unless he is a perfect citizen -- most parents don't think that way about their own children. I think that's outrageous."

Cynthia Gordy is The Root's Washington reporter.