A decisive shift toward construct validity as the central criterion for evaluating psychological measures emerged, reframing interpretation around what a test truly aims to measure rather than only observing correlations. Research practice increasingly integrated theory with measurement design, demanding study designs that reveal the relationship between test scores and underlying constructs. Standardization, reliability, and multifaceted validation became core concerns, aligning testing more closely with theoretical claims across disciplines. Historical Significance: The period solidified a paradigm in which validity and theory-driven interpretation guide instrument development, shaping decades of validation work and the everyday practice of assessment. Foundational instruments and critiques advanced the idea that measurement must be meaningful, generalizable, and grounded in broader psychological laws, influencing subsequent research in both clinical and educational psychology.