For meaningful learning to take place and to eliminate misconceptions, it is necessary to identify the process of conceptual change on any given topic. The research aims to examine the skills of science teacher candidates to prepare two-stage diagnostic questions on ‘Seasons, Climate and Weather Movements’. For this purpose, the research was carried out in 4 weeks with 40 (39 females, 1 male) second-grade science teacher candidates in the fall semester of the 2019-2020 academic year, using the holistic single-case study pattern of the ‘Observation-Based Case Study'. Tests prepared by pre-service teachers were applied to eighth-grade students. The 'Diagnostic Test Preparation Rubric' was collected using ”Concept maps“, ”Open-ended two-stage tests“ and ”Multiple choice two-stage tests". As a result of the descriptive and content analysis, it was noticed that teacher candidates are usually at an intermediate and good level in determining the propositions of knowledge about the subject, developing a concept map, and a two-stage diagnostic test related to the subject content.   Keywords: Diagnostic questions; science teacher candidates; seasons; climate; weather movements