The aim of this study is to develop a descriptive framework for teacher educators to assist teachers to plan and realize modelling implementations in their classrooms and for researchers to describe and analyse how modelling is implemented. The planning process and implementations of 12 middle and high school mathematics teachers who conducted modelling implementations were analysed by the researchers to achieve this aim. The data used in the study were lesson plans regarding each modelling implementation, the transcripts of the voice recordings of pre-implementation interviews with the teachers, transcriptions of the video recording of each implementation, and the observation notes of the researchers. The data were analysed within the framework of the grounded theory approach. All modelling implementations consisted of three main sections: planning, implementation, and assessment. The planning section includes identifying the goals, deciding the modelling task and making preparations. The implementation section consists of conducting warm up activities, sharing norms, sharing assessment criteria, presenting the modelling task and tracking students' work. The assessment section involves presenting solutions, discussing solutions and necessary revisions, assessing competencies, and sharing assessment results and arriving at decisions.