An elasticity solution for sandwich plates assembled with non-rigid bonding and subjected to edgewise loads is presented. The solution satisfies the equilibrium equations of the face and core elements, the compatibility equations of stresses and strains at the interfaces, and the boundary conditions. To investigate the effects of bonding stiffnesses on the responses of sandwich plates, numerical evaluations are conducted. The results obtained have shown that the bonding stiffness, up to a certain level, has a strong effect on the plate mechanical response. Beyond this level, the usual assumption of perfect bonding used in classical theories is quite acceptable. An answer to what constitutes perfect bonding is found in terms of the ratio of the core stiffness to the bonding stiffness.