This paper articulates features of Internet literacy practices that preservice mathematics and science teachers found compelling and important for their pupils' learning. As part of secondary mathematics and science methods courses, 24 mathematics and science preservice teachers (PSTs) conducted a scaffolded investigation into the literacy practices of pupils in their practicum placements. These investigations clearly demonstrated to PSTs that Internet literacies create new demands on comprehension strategies that are in some ways similar to traditional literacies but in many respects go beyond them. These new demands include how text is negotiated and how text is critically evaluated on the Internet. Further, the PSTs found that, despite general presumptions that today's pupils are adept at Internet use, the Internet places demands on pupils that they are often poorly prepared to engage. This study demonstrates that explicit instruction for both PSTs and pupils is needed in order to capitalize on the information potential of the Internet. In addition to reporting results and implications, the authors describe the investigation assignment and provide information that will enable interested researchers and mathematics and science teacher educators to adapt it for their own use. (Contains 7 tables, 1 figure, and 1 note.)