A provocative finding from developmental psychology research into variation in intervention response is that those children most at risk for adverse developmental outcomes are often the ones who benefit most from resources and services. This phenomenon has been termed “biological sensitivity to context” (Boyce & Ellis, 2005) or “differential susceptibility” (Belsky, Bakermans-Kranenburg, & van IJzendoorn, 2007). Sensitive/susceptible children are especially responsive to environmental stimuli both “for better AND for worse”: Under conditions of ample environmental resources and support, these children achieve better outcomes relative to less sensitive/susceptible peers; under conditions of scarce resources and inadequate support, these children experience adverse outcomes relative to less sensitive/susceptible peers. Initial formulations of this model focused on temperamental characteristics—personality-like traits of young children—as markers of sensitivity/susceptibility. Current differential susceptibility research is focused on genetic differences between individuals (Belsky, Bakermans-Kranenburg, & van IJzendoorn, 2007; Belsky et al., 2009; Belsky & Pluess, 2009). The best evidence for differential susceptibility—in which individuals who carry a particular genotype are both most likely to develop problems under adverse conditions and most likely to benefit from advantaged conditions—comes from studies
