The resurgence of social disorganization theory has been accompanied by the corresponding need to accurately and validly measure the level of community social organization. This study used an updated systemic model of social disorganization to examine neighborhood effect on both positive and negative youth outcomes. The study was conducted in a medium-sized Midwestern city with a population of approximately 127,000. A total of 103 tenth-grade males participated in the study along with 1 of their parents and 1 of their neighbors. The results demonstrated that sense of community (SOC) mediated the effect of neighborhood advantage on conventional activity. The action component of SOC mediated the effect of block stability. The findings indicate that youth reared in communities characterized by high levels of SOC were more likely to participate in prosocial behavior such as school activities. The study demonstrates that close-knit neighborhoods with high levels of SOC have important spillover effects in other youth developmental contexts. However, SOC did not significantly mediate the relationship between neighborhood advantage and self-reported delinquency. In conclusion, SOC was found to be a reliable and valid construct that could be used to measure the mediating variables of social disorganization theory; it taps into the important and subtle social processes that precede such collective behavior. Tables, appendices A-B, and references