This comparative case study describes the literacy practices of two groups of adolescents as they sought to solve authentic problems through engineering design processes. Three types of data were collected as the groups addressed these problems: video‐ and audio‐recordings of their conversations; adolescent‐generated products; and pre‐ and post‐challenge interviews. The authors used existing coding schemes of engineering design activity to identify when the adolescents enacted different stages of engineering design, as well as a modified form of constant comparative analysis to identify the literacy practices that corresponded with each stage. The analysis indicates that applications of literacy practices at each stage of the engineering design process enhanced the adolescents' overall design activity, whereas the absence of literacy practices often impeded the viability of their final designs. The authors suggest implications for high school engineering and science teachers who seek to enhance their students' design activity through literacy instruction.