**Supporting Data for "Teachers’ Perceptions of Mathematical Modelling Teaching in Junior High Schools in Beijing, China"**

As the process of analysing real-life problems or realistic situations using mathematical knowledge and methods, mathematical modelling is a popular educational activity in this rapidly developing society. Studies have been conducted on students’ performance in mathematical modelling activities or competitions, and empirical studies have been carried out regarding mathematical modelling competitions and solutions. Still, there is limited research on middle school teachers’ perceptions of mathematical modelling teaching clearly, considering mathematical modelling should be a part of educational activities at every level of mathematics education. This thesis aims to determine junior high school mathematics teachers’ perceptions of mathematical modelling teaching by addressing the following research questions: (1) What are the dimensions for teachers’ perceptions of mathematical modelling teaching based on extant literature? (2) How do teachers perceive mathematical modelling activities in junior high schools? (3) What are the potential factors that influence teachers’ practice-based perceptions of mathematical modelling teaching?

This thesis utilises mixed research methods involving three stages. Stage I involved the development of a Cognition-Attitude-Behaviour Model (CAB Model) based on a literature review for studying teacher’s perceptions of mathematical modelling teaching, referring to cognition perceptions, attitude perceptions, and behaviour perceptions as three dimensions of “teachers’ perceptions”. In Stage II, this thesis conducted a quantitative survey after developing a questionnaire with good reliability and validity to study mathematical teachers’ perceptions of mathematical modelling teaching. A total of 594 teachers were recruited from 78 junior high schools in Beijing. In stage III, a follow-up qualitative study comprising an analysis of lesson videos and a one-to-one semi-structured interview was conducted. A total of 28 participants from these 594 teachers volunteered to engage in an analysis of lesson videos, while 43 participants volunteered for a follow-up interview.

The findings are: (1) Cognition, attitude, and behaviour are three dimensions of teachers’ perceptions of mathematical modelling teaching; (2) Frontline teachers emphasise the necessity of mathematics modelling teaching in middle schools, citing curriculum standards. The segments of mathematical modelling and non-mathematical modelling are integral parts of a comprehensive mathematical lesson. Mathematical modelling competitions, problem-solving activities, STEM lessons and interdisciplinary lessons are the primary forms of mathematical modelling activities, emphasising student practicality, presentation skills, and teacher-student interaction; and (3) The influencing factors of teachers’ perceptions of mathematical modelling teaching are divided into six categories: (i) Gender, professional titles, and working experience, (ii) Internal factors from teachers, (iii) Student factors, (iv) School support, (v) Mathematical modelling teaching resources, and (vi) Educational policies of government departments.