After a grueling grading campaign, a chemist asked a writing and rhetoric specialist for help improving formal reports in the introductory organic chemistry lab. Together, we realized that the very best student reports employ many persuasive moves in the combined results and discussion subsection, whereas weaker papers omit the persuasive language. To make students aware of the need for persuasive language throughout their reports, we then developed a reworked assignment prompt and a lab-period-long workshop, in which we highlight persuasive moves by walking students through three key steps: oral argument, analysis of key rhetorical patterns (color-coded) that should be present in both a combined results/discussion section and an introduction section, and peer review for those key rhetorical patterns. Set in the context of discussions of the argumentative and rhetorical functions of each subsection of a lab report, this workshop helps illustrate the purpose to convince a skeptical audience of the most plausible interpretation of some collection of data behind many chemistry writing conventions. After the workshop, student work shows modest but visible improvement in their use of evidence in science writing: student understanding of their task shows appreciable (and appreciated) improvement.