The COSSAP provides grant funding and technical assistance to selected sites for the development and implementation of programs that address the issues and needs of children and families in which a parent has a substance use disorder (SUD). This article focuses on ways that schools can be partners with other agencies in addressing this issue. The rationale for such an effort is to enlist schools as partners with justice, public health, and child welfare agencies in addressing the effects on children of parental substance use. The COSSAP supports a model developed by the Centers for Disease Control and Prevention. It is called the Whole School, Whole Community, Whole Child (WSCC) model. This model uses an ecological, cross-system collaboration approach in addressing children's social, emotional, and physical well-being. In discussing factors in cross-agency collaboration, the article notes the importance of a clear division of responsibilities as agencies work toward the same goals. In addition to a general discussion of cross-agency collaboration, a separate section of the article discusses child welfare system considerations in supporting children whose parents have SUDs. "Spotlight" sections of this article describe features of specific COSSAP programs.