Research in the field of students' understandings of models and their use in science describes different frameworks concerning these understandings. Currently, there is no conjoint framework that combines these structures and so far, no investigation has focused on whether it reflects students' understandings sufficiently (empirical evaluation). Therefore, the purpose of this article is to present the results of an empirical evaluation of a conjoint theoretical framework. The theoretical framework integrates relevant research findings and comprises five aspects which are subdivided into three levels each: "nature of models," "multiple models," "purpose of models," "testing," and "changing models." The study was conducted with a sample of 1,177 seventh to tenth graders (aged 11-19 years) using open-ended items. The data were analysed by identifying students' understandings of models ("nature of models" and "multiple models") and their use in science ("purpose of models," "testing," and "changing models"), and comparing as well as assigning them to the content of the theoretical framework. A comprehensive category system of students' understandings was thus developed. Regarding the empirical evaluation, the students' understandings of the nature and the "purpose of models" were sufficiently described by the theoretical framework. Concerning the understandings of "multiple," "testing," and "changing models," additional initial understandings ("only one model possible," "no testing of models," and "no change of models") need to be considered. This conjoint and now empirically tested framework for students' understandings can provide a common basis for future science education research. Furthermore, evidence-based indications can be provided for teachers and their instructional practice.