Background: Since 2005, professionals in nine special schools collectively had developed an assessment tool called SCALES for all students regardless they are in special or mainstream schools in Hong Kong. Based on the concept of “one common curriculum for all”, SCALES is classified into the four Key Learning Area (KLA) strands of learning as in the mainstream curriculum framework, namely, Chinese, Science, Personal, Social and Humanities Education (PSHE) and Mathematics. This means that for the first time all of the students are being measured by exactly the same criteria irrespective of the ability or disability. Aims: In this study, we aim to apply Rasch measurement approach to analyzing a this innovative evaluation tool for children with special needs due to intellectual disabilities. Since Rasch measurement can convert ordinal measures into interval measures, the latter of which is fundamental for objective measurement in human sciences (Bond and Fox 2007). Methods: By using Winsteps, statistics such as infit and outfit mean square, person separation index, reliability, and dimensionality of the measurement scales are supported empirically. Results: The uni-dimensionality of the four major subject areas is supported with good psychometric properties such as high reliability and person separations that help differentiation of subjects. Selective applications of some items of these scales could be used by practitioners for quick screening and better intervention for care of children with special leaning needs. Conclusion: The scales are supported with both subject experts’ observation and quantitative evidence from sophisticated psychometric tests. Successful establishment of the instrument by subject experts is evident and quality-assured administration of the Rasch-based items in the future is recommended as the SCALES has proved to be a valid and reliable assessment measure for diverse learners.

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].