This article reports on the types of scientific writing found in two primary grade classrooms. These results are part of a larger two-year study whose purpose was to examine the development of informational writing of second- and third-grade students as they participated in integrated science-literacy instruction. The primary purpose of the present article is to report on the “genre set” (Bazerman, 2004) established in this community around science instruction. Using Halliday’s (1993) Systemic Functional Linguistics approach and Hasan’s (1985, 1994) Generic Structure Potential, I describe the genres of scientific writing and drawing activities in which these children regularly participated. Findings indicate that children participated in several distinct scientific genres, some of which were flexible, and some of which were highly constrained by the teachers. Each of the genres represented a distinct purpose, structure, and linguistic nature of scientific discourse. The influence of this particular genre set on children’s appropriation of scientific discourse is discussed.