Based on the framework of systemic functional linguistics (SFL), this study investigates the changes in foreign language (FL) writers’ genre awareness and meaning-making choices when instantiating the genre of summary over a semester-long course. The participants were 30 undergraduate students at different proficiency levels. The students’ developmental changes were analyzed using an in-depth qualitative analysis of their reflective comments in conjunction with their performances on pre- and post-instructional summary writing tasks. The findings indicate that as the students engaged in the SFL-informed genre analysis tasks, they began to explore not only ideational but also interpersonal and textual meanings, which are required to fulfill the rhetorical demands of summary writing. In addition, their lexicogrammatical choices also shifted toward more genre appropriate ones. However, proficiency effects were markedly observed in terms of how and to what degree the students were able to grammatically elaborate sophisticated expressions that help realize the genre. These findings highlight the importance of a SFL approach to teaching summary writing to FL writers. That is, although the degree to which students benefit from the tasks differs according to their proficiency levels, genre-specific language learning can be pushed by a SFL framework that enhances writers’ awareness of the tripartite interconnectedness among ideational, interpersonal, and textual meanings in specific FL instances, in this case, summary. This paper concludes that SFL can provide a renewed understanding of FL writers’ development and help writing-to-learn and learning-to-write fruitfully cross-pollinate to enhance the FL development of students.