This article is based on the text of the Gulliford Lecture given by Professor Harry Daniels at the University of Birmingham in October 2005. Professor Daniels takes, as his starting point, Ron Gulliford's assertion that teachers need to learn from their experience of trying to teach children who are "hard to teach." He goes on to look at the process of categorisation, which he identifies as a sociocultural and highly context-dependent process. Harry Daniels explores the pressures in favour of categorisation experienced by parents and professionals alike and notes some of the uses to which categorisations of learners are put. In concluding to his article, Harry Daniels contrasts the current rhetoric about the personalisation of learning with the kinds of "simplistic protocols or magic answers" that are often assumed to follow from categorisation. He argues that glib responses like these run counter to the reflective and dialogic principles established by Ron Gulliford and colleagues two decades ago.