Research Findings: Educational guidelines recommend a delayed, piecemeal approach to instruction on adaptation by natural selection. This approach is questionable given suggestions that older students' pervasive misunderstandings about adaptation are rooted in cognitive biases that develop early. In response to this, Kelemen et al. (2014) recently showed that young children can learn a basic yet comprehensive explanation of adaptation by natural selection from a picture storybook intervention. However, this research was conducted in a laboratory-based setting with children from middle and higher socioeconomic backgrounds. To further explore the intervention's efficacy, this investigation examined whether Kelemen et al.'s (2014, Experiment 2) findings extend to a more diverse sample of children tested in a more naturalistic setting, namely, after-school programs. After a 10-min picture storybook reading that described adaptation within a fictitious but realistic mammal species, 5- to 6- and 7- to 8-year-old children's learning of adaptation was examined. Results revealed that younger and older children benefitted from the intervention; however, older children displayed pronounced learning and generalization. Practice or Policy: Findings confirm that children are capable of learning complex biological ideas and that comprehensive storybook interventions are simple but powerful teaching tools. Implications for instruction on natural selection are discussed.