Scales of language proficiency provide “characteristic profiles of the kinds and levels of performance which can be expected of representative learners at different stages”(Trim,1978; see also North,2000).Among the scales reviewed by Han(2006)and Wang(2012),however,most are developed by an intuitive method with little empirical support and fail to pinpoint the underlying problems of language learners.This study will explore the scale construction from a cognitive-psychometric perspective,first by constructing a Q-matrix,the association between reading attributes and test items in reading comprehension,and then identifying the attributes that differentiate high-performing examinees from low-performing examinees on reading comprehension.Two characteristics are highlighted during the research: the thorough investigation of students reading comprehension process through Translog and a follow-up interview,and the polytomous coding of options in reading comprehension tests.Hopefully,the results will provide illuminating information in diagnosing high school readers strengths and weaknesses and thus help learners and teachers to remedy their learning deficits or to adjust their teaching schedules.