This study aimed to explore adolescent second language (L2) writers' composition across media (text-based writing and digital multimodal composing). The goal was to investigate how and under what conditions these writers used semiotic resources when they engaged in both text-based writing and digital multimodal composing. Grounded in the concept of adaptive transfer, this study was carried out in an after-school program at a secondary school in South Korea. The researcher conducted this study and taught the class sessions simultaneously. Three adolescent participants joined the program, wrote two text-based essays, and created two digital multimodal products. The researcher collected data from the interviews with each participant, class observations, and students' essays and products. Data analysis revealed that participants used and reshaped semiotic resources for both idiosyncratic and rhetorical purposes when composing across media. This paper offers suggestions for further research and outlines the educational implications of composition across media.