The study aims to examine two middle school mathematics teachers' implementation process of a mathematical modeling problem with their students in terms of planning of the implementation, teacher interventions in the implementation process and the teachers' evaluations of their implementation processes. This study was designed as a qualitative case study and conducted in 2018-2019 academic year. The participants of the study consist of two middle school mathematics teachers working in different public middle schools that are determined according to criterion sampling as one of the purposeful sampling methods. "The Sneakers Problem'' was implemented by the mathematics teachers in their classrooms. The data sources of this study were teachers' implementation plans, semi-structured interviews before and after implementation, audio and video recordings of the implementation processes. The findings showed that both teachers planned their implementations and carried them out within 80 minutes. Furthermore, the findings regarding the teacher interventions also displayed that diagnosis of students' thinking was predominant support as the intentions of the interventions and organizational support was predominant as the area of intervention for both teachers. On the other hand, the findings revealed although teachers encountered some negative situations during the implementations, they evaluated their first implementation process generally positive for both themselves and their students. The findings suggest that teachers need both practice and support for the process of applying the modeling problems in the classroom environment.