This book chapter describes an evidence-based, principles-focused developmental evaluation that was part of a larger grant program funded by the Otto Bremer Foundation, a private foundation serving the Minneapolis/St. Paul metro area. The foundation provided grants to six local youth-serving agencies to address youth homelessness in the Twin Cities. The developmental evaluation was initiated to create a process by which the six agencies could collaborate to improve the outcomes for youth and identify and empirically validate guiding principles. To meet these goals, the researchers engaged the foundation and agency leaders in collaborative evaluation inquiry during monthly reflective practice meetings, which included analyzing 14 youth case studies. The developmental evaluation process resulted in a principles statement and dissemination packet to be used by the agencies going forward. (author abstract modified)