Teaching a class of 33 girls any subject whatsoever would always be interesting, but when the subject is mathematics and when the exact nature of the course is left to the teacher, things become exciting! This was the case during the last term at a Girls’ Grammar School in Leicester where I was given a free hand to tackle any aspect of mathematics with the form 5Sc. Their average age was 15 (exactly: we had laboriously evaluated it the previous term when considering mean values!) and their ability was very high. Although they were still one year from O-level, I thought this to be an excellent opportunity for trying some “Modern Mathematics.”