A growing number of early childhood interventions are intended to be used by classroom teachers to support children's emergent literacy development, yet we know little about for whom such interventions might be effective. In this study, we examined whether children's initial emergent literacy skills (alphabet knowledge, phonological awareness, vocabulary) moderated the effects of a small-group emergent literacy intervention. Preschool children (M[subscript age] = 4.28 years) identified as at-risk for later reading difficulties (n = 281; 48% girls; 45% Black, 20% White, 13% Hispanic/Latinx) were randomly assigned to intervention conditions or a business-as-usual control condition. Using an instrumental variables approach to account for differences in intervention dosage, we found main effects of initial skills (ds = 0.07-0.27) but no evidence of differential response to intervention based on initial skills (ds < [vertical bar]0.01[vertical bar]). We call for further attention to this important issue in future intervention work.