Schools are complex systems, with diffuse goals and uncertain outcomes. Within schools, teachers have a pivotal role in the management of systematic learning in a social environment, in the maintenance of our culture, and in social reconstruction. For these reasons (and because teacher-salaries are a significant budget item) governments take a keen interest in the effectiveness of teachers and of schooling. Schooling is so complex that it is no longer possible to deduce systematic associations between the activities of the teacher and student learning. School learning is only one of a range of influences that impinge on the learner and it may well not be the most powerful influence. There is therefore, no simple cause and effect relationship between teaching and learning. Further, there are no standard indices of school effectiveness. Its assessment is largely a qualitative judgment. Assessments of effectiveness depend on clarifying the purposes of teaching. Until these purposes are known it is fruitless to investigate the effectiveness of teaching. Attempts to assess the effectiveness of schooling have not produced new perspectives, new knowledge or functional estimators. The outcome of a vast amount of research is enhanced expertise for those doing the research, and a set of generalisations that do not conflict with commonsense. In the most general sense the task of schooling is to prepare a nation's youth to be good citizens. The criteria for good citizenship vary from time to time and from country to country depending on the form of government, ideas about the model citizen and the state of the economy. Many governments treat teachers as implementation agents for their policies and they are judged effective to the extent that they act in accord with such policies. The paper explores these issues and examines implications for teacher education and schooling.