Strategic planning in school management now encapsulates a range of activities that are now required of staff in schools and, through school improvement planning, has come to be the only legitimate approach for schools in preparing for their future. Head teachers are central to this process. Consequently, they are now responsible for leading and managing their school's improvement by using pupil data to set targets for even better performance while being subject to inspection and the publication of inspection reports. This improvement in performance is concentrated on literacy and numeracy, expressed in terms of national targets. The work of head teachers is now firmly focused on the search for enhanced school success through strategic planning to improve both institutional and individual test and examination scores, coupled with the management of teacher performance. Success or failure will be determined by the extent to which schools meet these predetermined performance targets. Strategic planning for improvement in schools, therefore, is now perceived as both central to the implementation of the Government's educational policy and to the success of its wider economic and social agendas by providing a workforce with appropriate skills and producing good citizens. Is this confidence in the efficacy of this form of strategic planning justified or it is simply a name without a deed? The edifice of strategic planning in schools is based on a number of assumptions that can be seen as three sets of fallacies undermining its efficacy as a management technique for use in educational institutions. This article discusses these fallacies which take the form of assumptions about the nature of leadership, about planning as a management technique and about definitions of school effectiveness.