Did I read that right? School integration creates gangs?

http://www.nber.org/digest/may11/w16664.html

>Rucker estimates that each additional year of exposure to desegregated schools increased black men’s annual earnings by roughly 5 percent, increased their wages by 2.9 percent, and led to an annual work effort that was 39 hours higher. At the same time, for these black male adults the probability of poverty decreased by between 1.6 and 1.9 percentage points. Overall, five years spent in desegregated schools yielded an estimated 25 percent increase in annual earnings and increased annual work effort of 195 hours. Desegregation also resulted in significant long-run improvements in blacks' adult health, as measured by self-assessed general health status; the effect of a five-year exposure to school desegregation is equivalent to being seven years younger.

Some of the first American gangs were Irish (Forty Thieves, Dead Rabbits) and integration of the Irish in American society certainly didn't cause an increase in Irish street gangs.

I don't follow at all. You're blaming balkanization on integration? Sure, white flight was an unintended consequence but that surely wasn't the goal and no fault of the policy itself. And how is this connected to gangs? Gangs can't exist in segregated schools how?