We introduce an interactive tutor that supports the step-wise development of simple functional programs. Using this tutor, students receive feedback about whether or not they are on the right track, can ask for a hint when they are stuck, and get suggestions about how to refactor their program. Our tutor generates this semantically rich feedback from model solutions, using advanced concepts from software technology. We show how a teacher can add an exercise to the tutor, and fine-tune feedback. We report on an experiment in which we used our tutor.