Since the 1970s, school effectiveness research has looked for process-variables filling the black box between mainly structural school features and cognitive outcomes in students. Two concepts came to the fore: school climate and school culture. Both concepts are currently used interchangeably, although it is open to debate whether both are actually the same thing. Because of the way culture and climate are defined and subsequently measured, we propose school culture is a better frame from which to study school effectiveness. This article goes through the premises of perceptual measurement usually overlooked in climate research, and we demonstrate empirically by means of very basic and simple methods and techniques that perceptual measurement and measurement based on assumptions are different approaches and might yield totally different results on an aggregated level. We conclude by demonstrating how culture can be probed and integrated in the models traditionally used in school effectiveness research in an advantageous and theoretically sound way. (Contains 3 tables.)