High school English writing instruction faces persistent structural challenges, including vague argumentation, unorganised evidence, and broken reasoning chains. Existing pedagogical frameworks—process writing, genre-based pedagogy, and reading-writing integration—share a systemic gap in scaffolding students' argumentative logic. This paper conducts a theoretical investigation into the feasibility of integrating the Claim-Evidence-Reasoning (CER) framework into high school English writing instruction, using a Sports and Fitness thematic context drawn from the national PEP-A textbook series as an illustrative case. Drawing on a systematic review of recent empirical literature, the paper first examines the theoretical alignment between CER's three components and the core competences demanded by high school argumentative writing, demonstrating that Claim corresponds to thesis clarity, Evidence to the organisation of supporting details, and Reasoning to logical coherence and development. A three-stage instructional model (pre-writing, while-writing, post-writing) is then elaborated to operationalise the framework across the writing process. Pedagogical tools—including a Claim generation protocol, evidence classification scaffolds, Reasoning sentence starters, and a CER-aligned analytic rubric—are proposed and illustrated with topic-specific examples. The paper further discusses the complementarity of CER with existing frameworks, its comparative advantage over the Toulmin model in secondary school contexts, and its practical limitations with respect to genre range and grade level. The study contributes to the emerging body of cross-disciplinary research on CER and provides a theoretically grounded, practically operable blueprint for subsequent empirical investigation.