When we began to investigate the structure of classroom interaction we had no preconceptions about the organization or extent of linguistic patterning in long texts. Obviously lessons are highly structured but our problem was to discover how much of this structure was pedagogical and how much linguistic. It seemed possible that the presence of a linguistic introduction was a clue to the boundary of a linguistic unit, but we quickly realized that this is not a useful criterion. On the first morning of the academic year a headmaster may welcome the new pupils with

‘Good morning, children, Welcome to Waseley School. This is an important day for you…’

thereby introducing them to several years of schooling. When the children then meet their new class teacher she will also welcome them and explain their timetable. They go to their first subject lesson. Here the teacher may introduce the subject and go on to delimit part of it;

‘This year we are going to study world geography, starting with the continent of Africa…. Today I want to look at the rivers of Africa. Let’s start with the map. Can you tell us the name of one river, any one?’