The waggler, a neurological mutant mouse with a disrupted putative neuronal Ca(2+) channel gamma subunit, exhibits a cerebellar granule cell-specific brain-derived neurotrophic factor deficit, severe ataxia, and impaired eyeblink conditioning. Here, we show that multiple synapses of waggler cerebellar granule cells are arrested at an immature stage during development. Synaptic transmission is reduced at parallel fiber-Purkinje cell synapses. The Golgi cell-granule cell synaptic currents show immature kinetics associated with reduced gamma-aminobutyric acid type A receptor alpha6 subunit expression in granule cells. In addition, the mossy fiber-granule cell synapses exhibit N-methyl-D-aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs), but not alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated EPSCs. Our results suggest that voltage-dependent Ca(2+) channels are involved in synapse maturation. This deficient synaptic transmission in the waggler cerebellum may account for their behavioral deficits.