Everything starts with a problem and the aim of the disciplines is to find a proper solution for this current problem.  If one discipline is not enough to find this solution to create fresh uses and expressions, then the usage of more than one discipline is required for the solution of a problem which is called an interdisciplinary problem. In order to develop new applications and expressions, interdisciplinary research is seen as the merging of unique elements of more than one disciplinary subject in the search for fresh perspectives, useful uses, or artistic expressions corporately.  Moreover, it can be said that if there is more than one discipline utilizing by using a particular knowledge then it can be called interdisciplinary knowledge (Nissani, 1995). The curriculum addresses various elements of instruction, including the use of materials and technology, learning objectives, and assessment procedures. It also provides resources for instruction (Cohen et al., 2003). The IB-DP is a global curriculum that employs interdisciplinary methodologies. It is crucial to examine the manner in which interdisciplinary studies are integrated into the IB-DP curriculum and how courses facilitate this integration (IBO, 2023). Therefore, this study aims to explore Turkish IB-DP Mathematics teachers' conception of interdisciplinarity usage while teaching their lessons. The purpose of the current study is to explore participants’ experiences of the interdisciplinary perspective in teaching IB-DP Curriculum exponential function and assessment process. by using the model of interdisciplinarity of Williams and Roth (2019). Exponential function is one of the common topics for both standard level (SL) and higher level (HL) Analysis and Approaches mathematics of IB-DP. IB-DP curriculum discusses this topic to have links to other subjects in natural science (e.g. biology)  or social science (e.g. economy). The Mathematics: Analysis and Approaches Guide document provides suggestions for interdisciplinary connections for exponential function as “radioactive decay, charging and discharging capacitors (physics); first-order reactions and activation energy (chemistry); growth curves (biology).” (IBO, 2021, p. 40). The IB- DP assessment procedures evaluate the extent to which students have acquired advanced academic skills in fulfilling the aforementioned goals. These skills include the ability to analyze and present information, evaluate and construct arguments, and solve problems in a creative manner. In addition to these advanced skills, the assessment also gauges the acquisition of fundamental abilities, such as the ability to retain knowledge, comprehend key concepts, and apply standard methods. Furthermore, the assessment encourages an international outlook and intercultural skills, where appropriate. The assessment types of IB-DP are Internal Assessment (IA), Extended Essay (EE), and External assessment.

This study's primary purpose was to investigate Turkish mathematics teachers’ experiences of utilizing the International Baccalaureate Diploma Programme (IB-DP) interdisciplinarity while teaching exponential functions in mathematics. The data were gathered through two sequential semi-structured interviews. The first interview was conducted with eight teachers from Istanbul to examine their general conceptions about interdisciplinarity and IB-DP. The second interview was conducted with four teachers who were chosen among the first group to examine their instruction processes of exponential function and assessment process. The interviews were analyzed with (i)coding for teachers' conceptions of interdisciplinarity about instruction and (ii)thematic analysis. The study found that teachers are becoming interdisciplinary level for the instruction process and interdisciplinary level for assessment process by using the model of interdisciplinarity of Williams and Roth (2019).

Two phases of semi-structured individual interviews were conducted with participants for qualitative data collection tools. For the first phase, seven questions were formed to highlight the participants’ conception of interdisciplinary which is necessary for the instruction of IB-DP. The findings were evaluated according to Williams and Roth’s (2019) approach to interdisciplinarity for the mathematics teaching and assessment process of IB-DP. This approach has four levels: mono-disciplinary, multidisciplinary, interdisciplinary, and transdisciplinary. The findings revealed that four out of eight teachers’ instructional approaches were between multidisciplinarity and interdisciplinarity levels. None of the teachers were at an interdisciplinary level. The researchers named this position, between two levels, as becoming interdisciplinarity level. This finding was intriguing in a sense to examine further these teachers’ experiences of teaching interdisciplinary a mathematics topic. On the other hand, all of these four teachers are at the interdisciplinary level for the assessment process of IB-DP. Four IB-DP teachers were chosen from eight teachers who teach both standard level (SL) and higher level (HL) and work in both private and state schools in Istanbul. For this reason, a second semi-structural interview was conducted to understand how these four teachers incorporated their interdisciplinary insight into instruction. When validity and reliability are taken into account a study's quality rises. Trustworthiness was employed by Lincoln and Guba (1985) as a method for assessing the validity and reliability of qualitative research. For this reason, the data recorded and subsequently transcribed the interviews. To improve transferability, each analysis was given as much information as feasible utilizing quotes from the interviewees. Guba (1985) suggested looking at different types of data to help build credibility, so to ensure credibility, IB-DP Standards, books along with participant’s lesson plans. were examined. To enhance interrelated reliability, the member check method was employed by contacting each participant individually and asked whether the information they shared was comprehended correctly and whether they had any additional ideas to contribute. The interrelated method was satisfied by the member check method, which was used to verify the results. Lastly, as first author coded the data, the second author, more experienced researcher, guided the process by exchanging thoughts at each level of the analysis.

As a result of the second semi-structured interview focusing on the four participating teachers’ experiences on teaching exponential function with interdisciplinary approach of IB-DP three themes emerged: (i) modelling, (ii) conceptual understanding and procedural fluency, and (iii) the nature of school and for assessment process (iv) requirements of the IB-DP curriculum. (i) Modeling: All four teachers generally use an investigation activity to start the topic of exponential function. (ii) Conceptual understanding and procedural fluency: All four teachers start their exponential function topic by reminding prior knowledge which is related to function properties and exponential number properties. (iii) The nature of school: The nature and culture of schools are different from school to school since schools’ approaches, schools’ cultures and perspectives, school types, and teachers’ perspectives are different from each other. (iv) Requirements of the IB-DP curriculum: In this perspective, all four teachers explained the process by paying attention to what IA is, what are its criteria, what is expected from them, what is the purpose of IB-DP in this assignment, and why there is such an assignment. By doing that both Nil and Eren teachers give students an idea of creating a concept map based on theme of water which is given IB-DP sources explicitly.

Cohen, D.K., S.W. Raudenbush, and D.L. Ball, \Resources Instruction, and Research", Educational Evaluation and Policy Analysis, Vol. 25, No. 2, pp. 119-142, 2003. International Baccalaureate Organization. (2021). Interdisciplinary Learning in the International Baccalaureate. Retrieved from https://www.ibo.org/research/curriculum-research/cross-programme/interdisciplinary-learning-in-the-international-baccalaureate-2021/ International Baccalaureate Organization. (2021). Mathematics: analysis and approaches guide International Baccalaureate Organization. (2023). Why DP schoolwide? Retrieved from https://www.ibo.org/ib-schoolwide-adoption/a-more-inclusive-ib/why-dp-schoolwide/ International Baccalaureate Organization. (2023). Diploma Programme: Theory of knowledge guide. Retrieved from http://www.ibo.org. International Baccalaureate Organization. (2023). Creativity, action, service guide. Retrieved from http://www.ibo.org. Lincoln, Y. S., & Guba, E. G. (1985). Naturalistic inquiry. sage. Nissani, M. (1995). Fruits, salads, and smoothies: A working definition of interdisciplinarity. The Journal of Educational Thought (JET)/Revue de la Pensée Éducative, 121-128. Williams, J., & Roth, W. M. (2019). Theoretical perspectives on interdisciplinary mathematics education. Interdisciplinary mathematics education: The state of the art and beyond, 13-34.