In this study, how the learning process designed with mathematical modeling activities affects the mathematical modeling competencies of middle school students who are at different levels in terms of reading comprehension skills. In the study, nested (embedded) pattern was preferred among mixed method research designs. The participants of the study consisted of 26 middle school seventh grade students who were selected using the easily accessible situation sampling method, which is one of the purposeful sampling types. In the research, besides mathematical modeling activities, researcher and student diaries were used to obtain qualitative data on the functioning of the application process. "Modeling Activities Opinion Form" was also used at the end of the application process in order to determine the general views of the study group on the activities. The quantitative data of the study were collected through the "Reading Comprehension Test" and "Mathematical Modeling Competence Test", and the collected data were analyzed using both qualitative and quantitative data analysis methods. At the end of the study, it was determined that the mathematical modeling competencies of the students improved, but this development did not follow a stable course during the application process and the interpretation and validation competencies of the students were low.