Understanding Kids, Gangs and Guns I've been studying violent crime for more than a decade - first as an academic researcher, then briefly as a senior adviser to the F.B.I. - and have been struck by the ways in which our efforts to stop gun violence are not as targeted and efficient as they should be. Until I started observing gangs and criminals, I used to think that young, violent criminals were generally adept in gun use. I learned the reality was far worse. Gangs and drug crews had caches of high-powered weapons but no formal training. Their members could not match a gun to its proper bullet. Few knew how to load, clean or shoot. Their aim was woeful: they injured one another - not to mention bystanders - as often as their enemies. It would be ludicrous to train gang members to shoot better (even if it would reduce the number of innocent bystanders who get shot, it would empower criminals). So big-city mayors, and their police departments, understandably focus on gun access. But they have done so in an unbalanced way. Gun runners who transport weapons from federally licensed dealers to city neighborhoods have been singled out as a primary culprit. But purchases from authorized dealers account for only about 60 percent of gun purchases, and the gun runners - so-called straw purchasers - are responsible for only a fraction of these. We can no longer ignore the 40 percent of guns obtained on the secondary market, which includes gun brokers, gangs and other informal traders. For inner-city young men, a gun is a badge of honor and an act of masculine one-upmanship. Rarely do they have access to straw purchasers - most couldn't even name one. They do, however, know a gang or a clandestine seller around the corner from whom they can buy, borrow or rent a gun. Stopping the intra- and interstate transport of guns by straw purchasers can net great sums of money, not to mention public acclaim. But more significant gains have been made by targeting the secondary market, through amnesty programs in which guns may be turned in by the public, no questions asked. In June, for example, 5,500 guns (including some replicas and BB guns) were turned in to the Chicago police as part of its annual gun "buyback" program. The incentive? A $100 gift card for each real gun. Chicago's crime rate did not drop significantly as a result, but that is not the point of buybacks, which signal to communities that the police are interested in nonpunitive ways to get guns off the street. A second problem with current policy is the lack of support for mediation programs. In Boston, the interfaith Ten Point Coalition, co-founded by the Rev. Eugene F. Rivers with police support, helped reset relations between the community and law enforcement. Then the criminologist David M. Kennedy brought in his Ceasefire program, which brings street-based mediators and cops into productive discussions with gang members and would-be criminals. Gang violence sharply declined through both efforts, and Mr. Kennedy's experiment has been successfully replicated in other cities. But many police chiefs have been reluctant to embrace such efforts. They fear that mediators will usurp their authority and become vigilante citizen patrols. Charities are reluctant to support mediation efforts because of a mistaken view that philanthropy should not get into bed with law enforcement. The fact that criminal justice programs receive less than 1 percent of total philanthropic giving should alarm us. A third mistake: not understanding how guns change hands. A Justice Department study found in 2001 that 40 percent of all criminals acquired their guns on the street, but another 40 percent obtained their guns from friends or family members. Why not wage a national campaign around the familial dynamics that perpetuate liberal gun exchange? We are unlikely to eliminate guns from the home, but at least we could get out this message, through social media and clever advertising, that just as friends don't let friends drive drunk, they shouldn't lend or give weapons away. Acknowledging that many illegal guns will remain on the streets, while recruiting friends and relatives to at least make sure those guns are kept away from untrained and emotionally volatile kids, would be a sensible step. Good gun policy is good social policy. A study by researchers at the University of Chicago found that one-fifth of youths killed by gunfire there were innocent bystanders. The economist Steven J. Levitt has estimated that each homicide is associated with out-migration of 70 city residents. The total social costs of gun violence in Chicago have been estimated at about $2.5 billon - $2,500 per household - a year. I'm sure that Chicago's mayor, Rahm Emanuel, could find better ways to spend that money. Gun buybacks, mediation programs and media campaigns aimed at gun owners and their families should be among them. Sudhir Venkatesh, a professor of sociology at Columbia, is the author, most recently, of "Gang Leader for a Day: A Rogue Sociologist Takes to the Streets."