Much thought is being given at present to the possibility and desirability of introducing topics of modern mathematics, such as set theory and abstract algebra, into the sixth form curriculum. Very little of this kind of work has as yet been done in schools, chiefly because of its comparatively recent introduction into undergraduate courses, but it seems probable that it will come to play a part in the mathematical training of at least the abler boys in the fairly near future. Recently, during teaching practice, I had the opportunity of giving a course in group theory to four senior boys and I feel that the experience gained may be of interest to others who are contemplating similar kinds of work.