The researchers completed a corpus-driven analysis of 688 texts written for children, language learners, and older readers to determine the vocabulary size necessary for comprehension and the potential to incidentally learn vocabulary through reading each text type. The comparison between texts written for different audiences may indicate their relative value for use in extensive reading programs. The results indicate that a vocabulary size of 10,000 words plus knowledge of the proper nouns and marginal words was required to know 98% of the words in both text written for children and text written for older readers. In contrast, a vocabulary size of 3,000 word families plus knowledge of the proper nouns and marginal words was necessary to know 98% of the words in text written for language learners. Repetition of words in Nation's (2006) 3rd to 14th 1,000-word lists was higher in the text written for language learners, followed by children's literature and then text written for adults. The findings indicate that the lexical load of text written for children is similar to that of text written for older readers, and that neither of these text types is as well suited as graded readers for second language extensive reading. (Contains 6 tables.)