A Placement Diagnostic Instrument for the K-12 Informatics Pipeline: A Tool Design Specification

The Vietnamese K-12 informatics pipeline assembled by the elix-researches program spans four pathway series — From Scratch to Python (FS2P, Layer A), Python Pathway (PP, Layer B), Competitive Programming Pathway (CPP, Layer C with Spine-Cluster from Vol 5), and Document Engineering (DE, Layer H cross-cutting) — across roughly twenty-four published volumes covering ages eight to eighteen and beyond. A learner entering the pipeline at any of these layers requires a placement decision that is structurally heterogeneous: the entry construct at FS2P is computational-thinking literacy without text-code expectations, the entry construct at PP is reading-and-numeracy fluency plus optional prior-CS exposure, and the entry construct at CPP / Spine-Cluster is procedural fluency in a core construct set plus debugging-discipline and contest-session stamina. A single diagnostic instrument that routes across all three boundaries is required at the program level; node E1.5 (Python-Pathwayspecific placement) and node C3.1 (Spine-Cluster entry criteria) are sub-instruments scoped to one boundary each. This paper specifies the pipeline-level instrument: a three-band routing decision (low band, mid band, high band) inherited from E1.1, an item-bank skeleton differentiated by item type per band (tracing-only items at low band, modify-only items at mid band, write-and-trace items at high band), a scoring rubric mapped to bands, an adaptive routing decision tree that minimises items administered while preserving routing precision, a perband-criterion subscore reporting template, and an audit-loop hookpoint at each band boundary. The instrument is engineered against established psychometric criteria — content validity, construct validity, Cronbach internal-consistency reliability floor, time-bound deployability of thirty minutes or less, diagnostic-notsummative orientation, age-appropriate item phrasing per band, low-stakes deployment language, and an adaptable item bank that allows item rotation against exposure. Theoretical anchors include the ALEKS / Knowledge-Space-Theory adaptive-testing tradition of Doignon and Falmagne and Falmagne and colleagues, the Concept Inventory family from the Hestenes Force Concept Inventory through the Tew and Goldman Computer Science Concept Inventory work, the Lister tracing-and-reading study, the McCracken multi-institutional study, the Mead and Howell early programming-aptitude tradition, and Cronbach's reliability and validity frameworks. The deliverable is the instrument specification — design constraints, item-bank skeleton, scoring logic, routing tree, reporting template, audit hookpoints — not an empirically validated instrument. Per the program-level nocohort directive, validation comes from audit-loop review against the program rubric and from structured expert-panel review at the item level, not from cohort administration. Three open questions are flagged: cohort-validation pathways consistent with the no-cohort constraint, item-exposure management without a calibrated parameter pool, and the cadence at which the