This research examined how a specific reading purpose, i.e. introducing the text to elementary students, affects the readers' comprehension and how they write a text introduction. Participants were 11 graduate school students who were all native speakers of Japanese. The participants were asked to perform the following tasks: (1) evaluation of the degree of importance of each idea unit in the following cases: "overall understanding of the text" and "introduction of the text content to an elementary student", (2) writing a text introduction for elementary students, and (3) evaluation of their meta-cognitive activities while writing an introduction. There are 4 major findings: (a) in the rhetorical aspect, readers pay attention to the simplicity of the vocabulary, expressions, and structure of the text introduction, (b) content-wise, some participants added concrete examples easily understood by elementary students while some did not, (c) as a result of (b), the constructed mental representation can be divided into two levels: textbase and situation model, and (d) although the cognitive load is high, the act of introducing or explaining to others has a positive effect on one's own level of understanding since a more coherent representation is constructed.