The current investigation addresses critiques about motivation terminology and instrumentation by examining together three commonly used reading motivation assessments in schools. This study explores the distinctiveness and redundancies of the constructs operationalized in these reading motivation assessments with 222 middle school students, using item response theory. Results support distinctions between constructs grounded in self-determination theory, social cognitive theory, and expectancy-value theory as well as conceptual overlap, among constructs associated with competence beliefs and social sources of motivation across different theoretical traditions. Educational benefits of multidimensional and unidimensional interpretations of reading motivation constructs covered in these instruments are discussed.