A toilet training system comprises a seat (10) and a complemental base (12). The seat has a central seat member (34) with a curved surface defining a cavity shaped to accommodate a child, with an aperture (36) in its lower surface. The base comprises a cylindrical outer side wall (42) and a partition member extending transversely relative to the side wall to define a receptacle. The partition member has a central portion (50) with a surface which is inclined or curved complementally to the curved surface of the seat member. The seat can be mounted on the base in first and second configurations of the system. In the first configuration, the central portion of the partition member is located relatively close to the seat member, preferably touching it. This corresponds to a training or familiarising mode of use of the system. In the second configuration the partition member is spaced relatively further apart from the seat member, in which mode the system can be used as a potty. In a third mode of use, the seat can be mounted directly on the rim of a toilet.