Communities In Schools, Inc. (CIS) is a nationwide initiative designed to connect needed community resources with schools to help students, particularly those identified as at-risk, successfully learn, stay in school, and prepare for life. As part of a comprehensive 5-year national evaluation of CIS, ICF International conducted a school-level quasi-experimental study on 123 CIS high schools and 123 matched comparison high schools, using public use data from 7 different states. The study examined the differences in high school dropout and graduation rates between CIS and its comparison schools over a 4-year period, starting from the year prior to CIS implementation to 3 years after implementation. Our analyses showed that CIS high schools made stronger gains in on-time graduation rates, and had greater reductions in dropout rates, than comparison schools over the same period. Results were considerably stronger for CIS schools that implemented the CIS model with a high degree of fidelity. (Contains 8 tables, 2 figures, and 2 footnotes.)