Item Analysis of a High-Stakes Placement Assessment for Junior High School Students with Intellectual Disabilities

This study examines the psychometric functioning of the Basic Learning Ability Assessment (BLAA), a high-stakes placement assessment used in Taiwan’s Adaptive Guidance Placement System (AGPS) for junior high school students with intellectual disabilities (IDs). The sample comprised 203 ninth-grade students with ID from 47 public junior high schools in Taiwan, all of whom completed three operational multiple-choice forms of the BLAA. Using classical test theory (CTT), we examined item difficulty using proportion-correct indices, item discrimination using upper–lower group discrimination indices, distractor functioning by comparing response patterns between higher- and lower-performing examinees, and internal consistency reliability using the Kuder–Richardson Formula 20 (KR-20). The results show that most items fell within the average-to-easy range and demonstrated acceptable to strong discrimination. Distractor functioning was generally satisfactory, with most items containing no nonfunctioning distractors. KR-20 coefficients ranged from 0.904 to 0.926, indicating high internal consistency within each form. Functional Language and Social Adaptation showed relatively stable psychometric patterns, whereas Mathematical Skills displayed greater variability in item difficulty, discrimination, and distractor functioning. Overall, the findings provide initial CTT-based internal psychometric evidence regarding the item functioning and form-level reliability of the BLAA, while highlighting the need for ongoing item refinement, particularly in the Mathematical Skills domain.