This chapter concerns school improvement. It argues that, until recently, school improvement policies have either been created on little robust evidence at all, or have simply been based on the correlates of the kinds of school effectiveness studies described in the previous chapter. This is a very misleading approach because high- and low-attaining schools might differ in a range of ways that are unrelated to whether their results are better or worse. This includes their type (such as academy or community school), their location, and even their décor (potted plants for example). School improvement policies have also been influenced by highly vocal single studies, and developers acting as agents selling their wares via conferences and similar. Teacher action research is widely used but is not really research let alone action research as originally devised. As such, none of these are appropriate for advising national or local policy on improving schools.