The adult nervous system is plastic, allowing us to learn, remember, and forget. Experience-dependent plasticity occurs at synapses--the specialized points of contact between neurons where signaling occurs. However, the mechanisms that regulate the strength of synaptic signaling are not well understood. Here, we define a Wnt-signaling pathway that modifies synaptic strength in the adult nervous system by regulating the translocation of one class of acetylcholine receptors (AChRs) to synapses. In Caenorhabditis elegans, we show that mutations in CWN-2 (Wnt ligand), LIN-17 (Frizzled), CAM-1 (Ror receptor tyrosine kinase), or the downstream effector DSH-1 (disheveled) result in similar subsynaptic accumulations of ACR-16/alpha7 AChRs, a consequent reduction in synaptic current, and predictable behavioral defects. Photoconversion experiments revealed defective translocation of ACR-16/alpha7 to synapses in Wnt-signaling mutants. Using optogenetic nerve stimulation, we demonstrate activity-dependent synaptic plasticity and its dependence on ACR-16/alpha7 translocation mediated by Wnt signaling via LIN-17/CAM-1 heteromeric receptors.