The emphasis on language and literacy in science education research has urged science teachers to include reading as an integral part of learning science. However, in US secondary schools, the percentage of students reading under grade level is high, and emergent bilinguals (EBs) are significantly represented among this group. While researchers across disciplines have proposed a number of prescriptive reading practices in science classrooms tightly aligned with instructional standards, few scholars have closely examined the starting point of reading instruction in science classrooms, and even fewer have focused on actual instruction for EBs in these classrooms. This study examines the nature of existing reading practices in science classrooms, with a particular focus on EBs. Using a qualitative multiple case study method, this study found significant mismatches between actual classroom practices and the ideal prescriptions about science reading instruction portrayed in educational standards and research. This study also found that teachers were battling numerous obstacles to implementing research/standards-based prescriptions. With the implications of science reading instruction for EBs' language and science content learning, this article will contribute to developing reading instruction and practices grounded in real classrooms and improving the instructional environment for reading-inclusive science classrooms.