Residential child care workers, acting in loco parentis, are in continuous, daily contact with the children in their care, and as such they are one of the key support providers in their lives. However, there is little research on the extent of the support and contribution they make to the children’s well-being. This study examines the link between perceived staff social support and emotional and behavioral adjustment difficulties of adolescents in educational residential care settings (RCSs) designed for youth from underprivileged backgrounds in Israel. It also examines the moderating role of adolescents’ length of stay in the RCS in the link between staff support and adolescent adjustment. The study includes the reports of a random cluster sample of 1,409 adolescents in grades 8 to 12, residing in 16 Israeli educational RCSs. The adolescents reported an average of medium to high level of staff support. Being female, Israeli-born, and perceiving greater parental support were found to be positively correlated with perceived staff support. Staff support was associated negatively with adolescent adjustment difficulties, above and beyond the contribution of parents’ support. A significant interaction was found between length of stay and staff support in predicting adjustment difficulties. Specifically, among adolescents residing for longer periods in the RCS, there was a stronger link between staff support and fewer adjustment difficulties. The findings have implications for residential care policy and practice, especially regarding the need to strengthen the role of child care staff as a social support system for children and adolescents in residential care.