Factors affecting planning effectiveness in Hong Kong self-managing schools are investigated. Questionnaire survey data from teachers, gathered in late 1994 from schools participating in the Phases I & II of the School Management Initiative scheme, are analyzed by principal-components analysis and multiple regression. Flexible planning, teachers’ participation in planning, 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. As interactive model, “A self-Managing School Planning Model”, which is responsive, recurrent and flexible in nature, is proposed.