We use a Monte Carlo bond-switching method to study systematically the thermodynamic properties of a continuous random network model, the canonical model for such amorphous systems as a-Si and a-SiO$_2$. Simulations show first-order melting into an amorphous state, and clear evidence for a glass transition in the supercooled liquid. The random-network model is also extended to study heterogeneous structures, such as the interface between amorphous and crystalline Si.