Dendritic spines are postsynaptic compartments of excitatory synapses that undergo dynamic changes during development, including rapid spinogenesis in early postnatal life and significant pruning during adolescence. Spine pruning defects have been implicated in developmental neurological disorders such as autism, yet much remains to be uncovered regarding its molecular mechanism. Here, we show that spine pruning and maturation in the mouse somatosensory cortex are coordinated via the cadherin/catenin cell adhesion complex and bidrectionally regulated by sensory experience. We further demonstrate that locally enhancing cadherin/catenin-dependent adhesion or photo-stimulating a contacting channelrhodopsin-expressing axon stabilized the manipulated spine and eliminated its neighbors, an effect requiring cadherin/catenin-dependent adhesion. Importantly, we show that differential cadherin/catenin-dependent adhesion between neighboring spines biased spine fate in vivo. These results suggest that activity-induced inter-spine competition for β-catenin provides specificity for concurrent spine maturation and elimination and thus is critical for the molecular control of spine pruning during neural circuit refinement. Display omitted •Spine pruning and maturation in the mammalian brain are coordinated events•Competition for cadherins and catenins mediates spine maturation and elimination•Inter-spine competition for β-catenin in vivo biases spine fate during pruning•Activity-dependent acceleration of spine pruning and maturation requires β-catenin The pruning or elimination of dendritic spines is always coordinated with the maturation of surviving neighboring spines. This process is bidirectionally regulated by neural activity and mediated by inter-spine competition for cadherin/catenin cell adhesion complexes.