The theory of abstraction (A-theory) is a theory of learning and intelligence in general and of language acquisition in particular.A-theory uncovers the development of sign acquisition: From icon to index to symbol.Within each class of the trichotomy of the sign system, cognition of a sign moves from discrimination to prescission to hypostasis.To be specific, A-theory argues that language acquisition is a progressive process: 1.discriminative icon (percept →object): discriminated/bounded icon of objects;2.prescissive icon (image → percept);3.hypostatic icon (concept → object);4.discriminative index (icon → image or percept);5.prescissive index (image → percept);6.hypostatic index (concept → image or percept);7.discriminative symbol (linguistic sign → percept);8.prescissive symbol (linguistic sign → image);9.hypostatic symbol (linguistic sign → object).The current study examines the language development process using the A-theory.Implications for language assessment are also addressed.