During young adolescence, many youth develop strong identities in relation to science, technology, engineering and mathematics with computing (STEM + C). One way to design for student engagement in STEM + C is to create project-based units that leverage students' interests. We created one such unit, called the "smart greenhouse project". Drawing upon eight in-school-time and six out-of-school-time interventions, we present an instructional design case (IDC). In describing the Context, Final Design, Critical Decisions, Design Limitations and Reflections of this IDC, we highlight design considerations and limitations that may generate new understandings for educational designers engaging with this paper. Our main contributions center on modalities of computer coding, hybridity of instructional materials, flexibility of spatial orientations in computer-supported learning environments, near-peer approaches to teaching and mentoring and dispersed models of professional development. We hope to inspire educational designers to (re-)engage young adolescents in STEM + C learning, in ways that equitably foster youths' rightful presence.