We describe an intelligent tutor for programming embedded in a graphical programming language. The tutor monitors students' problem solving and provides feedback and guidance. Explanations are generated from the content of the ideal model's problem solving rules. The graphical interface is designed to facilitate the acquisition of causal models of programming. Students work in a medium that corresponds to their planning operations. The interface enables forward and backward chaining, thus conveying the structure of the planning more effectively than a text-based interface. The interface also provides a graphical record of the solution history and current goals.