This article reports on the development and testing of a questionnaire that can be used to measure the quasi-experimental attitude (QEA) of teachers. This attitude is reflected in the willingness of teachers to assess and organise their core activities (planning, implementing and analysing lessons) by analogy with experiments in the field of research, in order to gain meaningful experiences from this cyclical process, to evaluate critically these experiences and to draw from them conclusions on how to improve lessons in the future. The sample comprised 512 trainee teachers who had already been teaching independently for 15 months following the conclusion of their university studies. The analysis of the questionnaire showed that the reliability of the scale was satisfactory. Confirmatory factor analyses confirmed the assumption that the quasi-experimental attitude could be modelled in two ways: A first-order model with four intercorrelated factors (meticulous lesson planning, confidence in the predictability of how the lesson will turn out, evidence-based analysis of the lesson and scepticism about mere experience) and a second-order model in which these four factors are loading on the overarching factor QEA. Additionally, the instrument yielded plausible correlations to several validity criteria.