SUMMARY Compelling evidence links amyloid beta (Aβ) peptide accumulation in the brains of Alzheimer’s disease (AD) patients with the emergence of learning and memory deficits; yet a clear understanding of the events that drive this synaptic pathology are lacking. We present evidence that neurons exposed to Aβ are unable to form new synapses, resulting in learning deficits in vivo. We demonstrate the Nogo receptor family (NgR1-3) act as Aβ receptors mediating an inhibition of synapse assembly, plasticity and learning. Live imaging studies reveal Aβ activates NgRs on the dendritic shaft of neurons triggering an inhibition of calcium signaling. We define T-type calcium channels as a target of Aβ-NgR signaling, mediating Aβ’s inhibitory effects on calcium, synapse assembly, plasticity and learning. These studies highlight deficits in new synapse assembly as a potential initiator of cognitive pathology in AD, and pinpoint calcium dysregulation mediated by NgRs and T-type channels as key components.