It is hypothesized that variability found in the effects of family literacy programs results from differences in implementation by parents. In this study, the implementation and effects of a Dutch program were examined in a sample of 207 kindergarteners (mean age at pre-test: 64 months). No main intervention effects on children’s literacy development were found. The quality of implementation proved to be higher for high-SES and native Dutch (speaking) parents than for low-SES, ethnic-minority parents with other home languages. Parent SES, ethnic-minority status, and home language did not moderate the program effects on child language scores and the program failed to impact targeted parental attributes, namely, the home literacy environment and parent self-efficacy. Finally, children’s development proved unrelated to implementation variables. Our results stress the importance of delivery for adequate implementation.