Several hypermedia learning environments have been developed in the last years, with the objective of helping students to acquire specific concepts on a given topic, as well as problem-solving abilities. However, there are still many different and sometimes conflicting claims about learning effectiveness by means of such environments. We present an empirical evaluation of a learning hypermedia with a tutorial component that exploits Artificial Intelligence techniques. This hypermedia, called Logiocando, has been designed to be used by a special category of users, namely children of the fourth level of primary school, to help them to learn basic concepts of logic. This category of users demands special attention to usability of the hypermedia. For this reason, project and development of the hypermedia have been carried out following a strict user-centred methodology, in order to build a system that satisfies clear usability objectives. The aim of the controlled experiment here reported was to evaluate the learning effectiveness of Logiocando and to estimate the difference between two approaches: the computer-based one, that uses a hypermedia system, and the traditional one, that uses the typical lesson in classroom. The results have shown that the hypermedia can certainly be considered a valid support in the process of learning and deepening a topic.