This special issue of the International Journal of Designs for Learning will focus on implementations of instruction, specifically on designs intended for (or used by) K-12 learners. The editors view educators as designers, and this issue will bring to our field the standard of precedent-building common in other design disciplines, fostering deeper understandings of designs and implementations within classrooms of all kinds in order to build our collective knowledge of what has gone into, and been realized with, our designs. These will not be documented as a traditional research paper, but the form of knowledge-building expressed as a design case, as detailed in the full call. We are particularly interested in papers authored or co-authored by teachers.