Despite high-level policy documents emphasizing its transformative role, educational assessment remains trapped in traditional epistemological presuppositions that prioritize measuring mental contents and internal representations. This gap necessitates a fundamental redefinition of assessment. Drawing upon Wittgenstein's later philosophy—particularly "language-games," "meaning as use," "hinge certainties," "family resemblances," critique of "causal explanation" and "inner processes," and the "therapy" metaphor—this study employs an analytical-inferential method to systematically redefine educational assessment. Findings indicate that authentic assessment must shift focus from testing mere naming of concepts to examining their situated application within "forms of life." Error should be regarded not as deficiency, but as a clinical symptom for diagnosing conceptual confusion. Assessment must move from psychological causal explanation toward phenomenological description of action, and by embracing ambiguity, it should be grounded in a "pedagogy of ambiguity" rather than a "pedagogy of certainty." The ultimate conclusion is that assessment must transform from a classificatory tool into an opportunity for "mutual understanding" and a "therapy of understanding." Consequently, the teacher's role should evolve from an "impartial judge" to an "authentic witness of understanding" within a "conversational companionship." This transformation repositions assessment from the margins to the center of educational development, cultivating critical thinking, creativity, and situated application of concepts in real life.