As we begin the third decade of the twenty-first century, in countries where English is the second or foreign language, the goal of internationalization is causing a rise in university first language-English bilingual science courses. Even though bilingual written scientific argumentation (BWSA)--a twenty-first-century skill--is an essential aspect of bilingual scientific literacy (BSL), little is known about how to promote this skill in this type of courses. The purpose of this study was to provide research evidence that formal formative assessment (FFA) could be a possibility for promoting BWSA among university students. A FFA-based pedagogical strategy involving preplanned feedback and peer critique was implemented with fifty-seven students (32 females and 25 males, 16-24 years old) in Colombia during a university Spanish-English bilingual science course. The data were derived from undergraduate students' written productions in Spanish and in English. The results demonstrated that the pedagogical strategy can be useful for providing students with explicit opportunities to enrich their BWSA. This study contributes to the construction of research-based bilingual practices aimed at legitimating BSL and BWSA in university bilingual science courses. Implications for higher education institutions are discussed.