In discussions about transformational leadership theory, three conceptions frequently emerge: (a) principals' transformational leadership behaviours are more prevalent in national contexts that are restructuring-oriented; (b) principals' transformational behaviours are more effective than transactional behaviours; and (c) principals are either transformational or transactional. These conceptions are repeatedly addressed but seldom explored in an empirical manner. Accepting conceptions as given might result in flattening scholarly discourse and depriving practice of research knowledge. The present paper aims to investigate these conceptions based on data derived from published works and from the author's database. The results of the investigation suggest that conceptions about principals' transformational leadership in education are unsupported by empirical exploration. Educational leadership research may be improved by periodically subjecting conceptions to empirical test, and incorporating in future works only those that show empirical support. Such exploration is necessary to maintain relevance in an applied research field such as education.