AbstractIn this randomized controlled trial, 508 5-year-old kindergarten children participated, of whom 257 were delayed in literacy skills because they belonged to the lowest quartile of a national standard literacy test. We tested the hypothesis that some children are more susceptible to school-entry educational interventions than their peers due to their genetic makeup, and thus whether the dopamine receptor D4 gene moderated intervention effects. Children were randomly assigned to a control condition or one of two interventions involving computer programs tailored to the literacy needs of delayed pupils: Living Letters for alphabetic knowledge and Living Books for text comprehension. Effects of Living Books met the criteria of differential susceptibility. For carriers of the dopamine receptor D4 gene seven-repeat allele (about one-third of the delayed group), the Living Books program was an important addition to the common core curriculum in kindergarten (effect size d = 0.56), whereas the program did not affect the other children (d = –0.09). The same seven-repeat carriers benefited more from Living Letters than did the noncarriers, as reflected in effect sizes of 0.63 and 0.34, respectively, although such differences did not fulfill the statistical criteria for differential susceptibility. The implications of differential susceptibility for education and regarding the crucial question “what works for whom?” are discussed.