Extensive experience in written language might provide children the opportunity to learn to read in the same manner they learn spoken language. One potential type of written language immersion is reading aloud to children, which is additionally valuable because the vocabulary in picture books is richer and more extensive than that found in child-directed speech. This study continues a comparison between these 2 communication media by evaluating their relative linguistic and cognitive complexity. Although reading grade level has been used only to assess the complexity of written language, it was also applied to both child-directed and adult-directed speech. Five measures of reading grade level gave an average grade level of 4.2 for picture books, 1.9 for child-directed speech, and 3.0 for adult-directed speech. The language in picture books is more challenging than that found in both child-directed and adult-directed speech. It is proposed that this difference between written and spoken language is the formal versus informal genre of their occurrence rather than their text or oral medium. The value of reading books aloud therefore exposes children to a linguistic and cognitive complexity not typically found in speech to children.