Abstract. We present an overview on the AT(x) approach which is capable of automatically analyzing programs with respect to given tests and a reference solution. In the context of small homework assignments with precisely describable tasks, AT(P), a Prolog instance of the general AT(x) framework, is able to find many of the errors usually made by students and to communicate them in a manner understandable for beginners in Prolog programming. The system is being used in distance education where direct communication between students and tutors is most of the time not possible.