The SCALE, an assessment instrument to align assessment with the central curriculum for pupils with intellectual disabilities was developed by a team of teacher leaders from nine special schools in Hong Kong. This study aims to report on the psychometric properties of the SCALE using Rasch analyses. Results indicate that SCALE possesses a high degree of validity and reliability. It can classify pupils into at least 13 levels of abilities, and that the range of item difficulty is capable of stratifying pupils' abilities into at least 8 to 11 attainment levels. Uni-dimensionality of the SCALE was also established. The use of SCALE in providing evidenced-based outcome data to document progress of pupils across their years in education, and, to inform school-based curriculum planning, is discussed. Impact of a well-validated curriculum-based assessment measures on accountability from the perspectives of assessment of learning and assessment for learning are also considered.[Copyright © CONFAB JOURNALS].