This paper reports on an investigation into factors affecting planning effectiveness in Hong Kong self-managing schools. Questionnaire survey data from teachers in schools participating in the Phases 1 and 2 of the School Management Initiative scheme in Hong Kong, are analysed. Principal's support and resource support are found to be significant factors in predicting positive outcomes of planning. The concept of flexible planning is explored and conceptualized in terms of built-in flexibility and flexibility through evaluation. An interactive model, `A Self-Managing School Planning Model', which is responsive, recurrent and flexible in nature is proposed. Copyright © 1998 British National Leadership, Management and Administration Society.