The eight organizations: parents' groups, civic groups, local businesses, churches, social services, mental-health providers, juvenile justice agencies, and the police.
Discussion
Put the two findings together. Schools in areas their principals call high-crime work with more outside organizations, and with more of every kind, not only more police and courts.
That fits what Patrick Sharkey has shown about American cities: the response to violence over the last thirty years came substantially from community organizations rather than from policing alone. Our result runs the other way round from his, and it is not causal. A school in a violent area holds more ties to the same kind of organization he identifies, and no more to the police.
The two explanations come out differently for the people and for the institution. Where principals report more crime, parents turn up to school events considerably less often. That is Wilson's social isolation, and social capital predicts it. The school itself works with more organizations, and resource dependence predicts that. The people and the institution among them run in opposite directions, in the same places at the same time.
The advantage test is the cleanest thing here. If a wide network were a mark of doing well, the schools with the most advantaged students would have the widest networks. They do not. Entered together, no measure of the student body can be told apart from zero, and the two closest run the wrong way for that account.