In general, where a case study is undertaken by a teacher in context-directed mode (to address issues and problems identified in practice, see Figure 5.2), it is likely to be an intrinsic case study. Where, instesd, a teacher is interested in learning more about how some general theoretical issue (dialogic teaching, student misconceptions, formative assessment, student understanding of multiple representations, etc.) links with their professional practice, they may select a particular case (e.g., teaching a particular topic with a specific class, or a suitable lesson for group discussion work, etc.) because they think it is a suitable context for exploring the issue. So where a teacher-researcher selects one class, one lesson, one topic, one group of students, as a suitable context for under taking theory-directed research (see Figure 5.1), rather than because the issue derives from concerns about that class, topic, etc., then we would consider this an instrumental case study.