Designing an Unplugged-to-Python Bridge for a Dual-Reader Textbook: the Vol 0 to Vol 1 Transition in the Python Pathway

Textbook series that cross the unplugged-to-text boundary in K-12 informatics face a design problem that the block-to-text transition literature only partially addresses: an unplugged first volume imposes no executable semantics, so the second volume must introduce both syntax and a first runningcode semantics simultaneously. We describe the design of the Vol 0 to Vol 1 transition in the Python Pathway, a Vietnamese K12 informatics textbook series built around a Star Topology Skills architecture. Vol 0 is a fully unplugged computational-thinking volume for Grades 3–5; Vol 1 is the first Python volume for Grades 5–12. Vol 1 Chapters 1–3 re-use Vol 0 scenarios (numericcard manipulation, roster-based roll-call, line-ordering) as a pedagogical bridge: readers who completed Vol 0 benefit from reduced intrinsic cognitive load while direct-entry readers (including upper-secondary self-directed learners) are not infantilised by primary-school imagery. We synthesise six design principles from dual-modality transition work, mutual-translation bridge pedagogy, PRIMM, subgoal labelling, cognitive load theory, and backward design. We present a scenario portability matrix, a chapter-level re-use strategy, an age-neutral voice calibration, and a low-N adult-proxy feasibility pilot specification consistent with the program's no-cohort-work constraint. The contribution is a reusable transition-design pattern for dual-reader informatics textbooks and a pilot protocol adapted for no-minors research scope.