Children who attend school with many kids from violent neighborhoods can earn significantly lower test scores than peers with classmates from safer areas, according to a new Johns Hopkins University study.

In schools where more kids have a high exposure to violence, the study found, their classmates score as much as 10 percent lower on annual standardized math and reading tests. The findings, which demonstrate how urban violence and school choice programs can work together to spread "collateral damage," appear today in the journal Sociology of Education.

"Exposure to neighborhood violence has a much bigger impact that we think it does," said the lead author, Johns Hopkins sociologist Julia Burdick-Will. "It seeps into places that you don't expect. It can affect an entire school and how it's able to function."

Burdick-Will studied students who attended Chicago Public Schools from 2002 to 2010, analyzing administrative data from the school system, crime statistics from the Chicago Police Department and school surveys from the University of Chicago Consortium on Chicago School Research. She looked at five cohorts of students who were freshmen between the fall of 2002 and 2006, and followed each student for up to four years.

She found high school students in Chicago public schools experience, on average, about 70 violent crimes a year within a few blocks of their homes. Children with high levels of exposure to violence, however, often experienced double that.

The crimes included homicides, sexual assaults, aggregated and simple batteries, aggravated and simple assaults, and robberies.

About half of the students studied were African American and about a third were Hispanic. Schools with students who experienced high levels of neighborhood violence, however, were more than 94 percent African American.

Because Chicago offers students the option of attending school anywhere in the city, students often commute to schools across town. Students from nearly every neighborhood attend nearly every school. This means that the experience of violence that Chicago students face where they live does not necessarily remain in their neighborhood, but is taken with them all over the city where they attend school.

Previous research shows that children living in violent neighborhoods experience trauma that makes them more difficult to teach and is related to an increased likelihood of high school dropout and low test scores as well as depression, attention problems, and discipline issues, says Burdick-Will. What hasn't been studied in the past is that students who are in the same classes as these children also don't learn as well, scoring as much as 10 percent lower on annual tests, she found.

It's possible these effects build over time, she says.

"This is just one year -- we don't know what the cumulative effects are," Burdick-Will said. "If you score 10 percent lower in just one year, you're that much less prepared for the next year. Ten percent less growth in a year is a pretty big deal."

Chicago's crime rates are comparable to those in Baltimore, St. Louis, Philadelphia, Houston and Miami, and it is possible that schools in those cities have similar issues, Burdick-Will says.

"Dealing with urban violence has ripple effects we're only starting to understand," she said. "We can't think about violence as something happening to kids in an isolated part of the city where I don't live. That's just the tip of the iceberg. High crime rates may be concentrated in specific areas, but their effects can be felt in schools all over the city."

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This work was supported by the Institute for Educational Sciences, the Population Studies and Training Center at Brown University, and the Hopkins Population Center.