The neuronal immediate early gene Arc plays a critical role in synaptic plasticity and homeostatic scaling by regulating AMPA receptor trafficking. We previously proposed the inverse synaptic tagging mechanism of Arc for synapse‑specific AMPA receptor regulation. As follow‑up studies, we investigated subunit‑specific AMPA receptor regulation by Arc during structural plasticity in cultured hippocampal neurons. Long‑term potentiation (LTP) of surface GluA1/GluA2 levels in spines with volume expansion was undistinguishable between wild-type (WT) and Arc‑knockout (KO) neurons. However, consistent with the inverse tagging of Arc to weak synapses, surface GluA1/GluA2 complex gradually decreased in non-expanding spines of WT neurons during the late phase of structural plasticity, and this effect was abolished in Arc‑KO neurons. Interestingly, in contrast, LTP of surface GluA2/GluA3 levels showed a significant increase in Arc‑KO neurons in expanded spines immediately after structural plasticity, while no effect was observed on non‑expanded spines. Thus, disruption of Arc orthogonally affected distinct of AMPA receptor compositions during early and late phases of LTP in potentiated and non‑potentiated spines, without affecting plasticity induction per se. These findings strikingly correlated with the normal acquisition yet dysfunctional behavioralrefinement in Arc-KO mice in two independent target-switching tasks. Network analysis of behavior during the task demonstrated a deficit in target precision in Arc‑KO mice. Our findings suggest a novel synaptic mechanism by which Arc expression regulates cognitive refinement processes such as memory precision and behavioral flexibility.