The Children’s Bureau, within the Administration for Children and Families (U.S. Department of Health and Human Services), funded a multi-phase grant program to build the evidence base on what works to prevent homelessness among youth and young adults who have been involved in the child welfare system. Known as Youth At-Risk of Homelessness (YARH), this program funded 18 organizations for the first phase for two years. During the planning phase, grantees conducted data analyses to help understand their local population and develop comprehensive service models to improve outcomes in housing, education and training, social well-being, and permanent connections. For the second phase, six of the 18 organizations received funding to refine and test their comprehensive service models with a three-year implementation grant. This issue brief describes the challenges, lessons learned, and next steps of one grantee—United Way of King County in Washington. (author abstract modified)