That writing can support students' learning in science and mathematics has been documented, yet little is known about how empirical findings have been applied in (1) materials designed to support science and math instruction; and (2) informal learning environments mediated by peer instructors. This dissertation examines two relatively unexplored aspects of content-area writing holding implications for advancing the use of writing as a knowledge-building tool: (1) how participants practice scientific literacy in the forum boards of a virtual open educational resource (Khan Academy); and (2) how writing is used in popular Open Educational Resource science and math curricula. The three related dissertation studies employ a combination of qualitative linguistic and content analysis within a conceptual framework of disciplinary literacy to explore the role of writing in the teaching and learning of "disciplinary literacy": 1) How do participants practice scientific literacy in forum boards of a virtual open educational resource? 2) What does a linguistically informed content analysis of publicly available digital math curricula reveal about: (a) the characteristics of writing tasks designed to support students' learning of mathematics content and mathematical thinking; and, (b) the nature of scaffolding of writing within these tasks?; and 3) What does a linguistically informed content analysis of publicly available digital science curricula reveal about: (a) the characteristics of writing tasks designed to support students' learning of science content and scientific thinking; and, (b) the nature of scaffolding of writing within these tasks? Findings show that: (1) Virtual learning environments promote cognitive apprenticeship opportunities supporting scientific literacy through peer-mediated discourse; (2) Math OER materials allow students to engage in multiliteracies, but opportunities for extended writing are limited; and (3) Science OER materials emphasize literacy opportunities and inquiry. Limited use of rubrics, writing models, and tools to support math and science teachers with explicit writing instruction was evident. These findings may help inform future research on, and development of, curriculum and teacher development to support disciplinary writing in science and mathematics. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]