This thesis uses a case study approach to show how a strategy of 'School Development' might be applied to New Zealand schools. It is argued that a policy of school based staff development and training will lead to greater school effectiveness. Such a policy uses a coordinated organizational approach rather than the more traditional reliance on withdrawing teachers from their classrooms for a time in order to concentrate on elements of the teaching-learning process. Support for this concept is derived from Organization Development theory and research. The term 'School Development' has been used to distinguish the particular New Zealand modifications which have been made to the more generic organization development theory. The notion of a consultant is central to the approach described and tasks and procedures which would be used by interventionists are discussed. School development assumes that schools have the capacity for self renewal. The consultant merely helps the school to realise this capacity. Components of teaching practice can be addressed within the framework of the school where they occur. Teachers can in this way increase their effectiveness with their present classes. The study concludes with a discussion of the implications of school development for teacher education generally.