This article focuses on the variability in developmental outcomes of foster children and the implications for foster care research and practice. We first provide a brief overview of our previous work, where we have shown by means of meta-analysis and a longitudinal study that foster children greatly vary with respect to their developmental functioning. We then discuss that it is both the heterogeneity of developmental trajectories and the lack of an accurate model for predicting foster children's development that make the screening and monitoring of foster children's development important. We provide suggestions for screening and monitoring, and discuss the Brief Assessment Checklist as an example of a specific instrument available for screening and monitoring of vulnerable children exposed to severe social adversity. We conclude our article with directions to improve foster care and research on foster care, including a discussion of the effectiveness of and foster children's susceptibility to interventions, support for foster parents and the potential of large national and international studies.