Skill-Band Definitions Across the K-12 Informatics Pipeline: A Cross-Paper Synthesis

The elix-researches program produces a K-12 Vietnamese informatics pipeline ranging from unplugged primary literacy (FS2P Vol 1, ages 8–11) through contest-competent specialised secondary practice (CPP Vol 7–8, Spine-Cluster training for ages 16–18). Across this pipeline the program has accumulated, by 2026-05, a Layer A–D research portfolio of more than thirty paper-grade nodes specifying foundation, consolidation, specialisation, and competitive-track pedagogy. Each layer references skill states implicitly — "syntax-aware", "function-fluent", "recursion-ready", "Spine-Cluster entry" — but the program has not until now defined the skill-band system that the layers populate. This paper specifies that system. The contribution is a descriptive seven-band schema (B0 First-Encounter, B1 Syntax-Aware, B2 Construct-Fluent, B3 Function-Decomposition-Ready, B4 Algorithm-Vocabulary, B5 Spine-Cluster-Entry, B6 Contest-Competent) derived bottom-up from the skill descriptions in the Layer A–D papers, grouped by ability cluster, with boundaries calibrated against external proficiency-threshold systems (Anderson's ACT-R thresholds, the Doignon-Falmagne knowledge-spaces, Bloom's revised cognitive taxonomy, the Dreyfus five-stage skill-acquisition model, ACM/IEEE CC2020 assessment bands, the IOI Syllabus 2024 difficulty bands, the USACO Bronze/Silver/Gold/Platinum divisions, the NRC Foundations of Software Engineering framework, the CSTA K-12 Computer Science Standards bands, and Wing's computational-thinking framing). Each band is presented with name, typical age window, six to nine observable behaviours, transition-to-next-band markers, a mapping to specific FS2P / PP / CPP volumes, a mapping to external systems, and an audit-rubric stub for the program-level audit loop. The system is engineered for descriptive utility (placement, curriculumdesign audit, cross-paper coherence checking) rather than for certification; it is the construct-map input that the E1.5 placement diagnostic [1] consumes for its routing decisions, and the construct-map output that downstream node E1.2 (placementdiagnostic operationalisation per band) and E4.4 (star-topology assessment) will consume. Four open questions are flagged for downstream Layer E research: whether the system survives as continuous-scale calibration data accumulate, whether a sub-band granularity (e.g., B2a/B2b) is needed inside the Vol 1–2 transition, whether B4 needs a split between recursivevocabulary and graph-vocabulary, and whether a Vietnamesespecific competitive-culture refinement is required at B5–B6.