Öz
This study aims to develop a valid and reliable measuring instrument that can measure the level of mathematical language used by students and their teachers during the teaching of fractions to fourth-grade primary school students. This study is a methodological validity and reliability study. In total, 999 students from fourteen different secondary schools were separated into two other sampling groups, where they participated in the sample of the survey for Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA). These stages are identified as the item pool stage, the testing validity of scope stage (expert opinion stage), the factor analysis stage (construct validity), and the reliability stage. Mathematical language scale in the teaching of fractions consists of the student approach, the use of fraction language and the use of symbols, and the written expressions of sub-dimensions. The exploratory factor analysis method (EFA) shows that the instrument can be built on three factors. It is also confirmed by the confirmatory factor analysis (CFA). It can be accepted according to NFI indexes. As a result, the mathematical language scale is found to be valid and reliable in fraction teaching. To this end, it can be stated that the MLSFT scale can be used in fraction teaching for elementary school students to reveal their abilities and the skills of teachers in terms of mathematical language used.