EXPLORATION OF LEARNING OBSTACLE BASED ON MATHEMATICAL UNDERSTANDING OF ALGEBRA IN JUNIOR HIGH SCHOOL. The difficulty of students related to algebra arises from the lack of students' mathematical understanding and Learning Obstacle (LO). One of the LO's experienced by students is the epistemological obstacle in the form of the limited knowledge possessed by students in mathematical concepts related to algebraic form. The purpose of this study is to explore LO related to algebra material. This research method is qualitative with the consisted of 15 students of 7th grade. The results showed that the common students could not interpret concepts and clarify the elements of algebraic forms related to variables, coefficients and constants and students could not operate and simply algebraic forms. The teacher can make pedagogical and didactic anticipations to overcome the LO.

This research is motivated by the importance of students 'mathematical understanding, but the fact is that students' mathematical understanding is still low in working on algebraic form questions. This problem brings out a learning obstacle, where students cannot interpret the algebraic form elements and cannot operate the algebraic form. This study aimed to design a didactic design phase using fables based on students' mathematical understanding. The research method is descriptive qualitative research. Design is Didactical Design Research (DDR) with 15 junior high school students as subjects. The data was collected using triangulation techniques, then analyzed descriptively. This study results in a didactic design in the form of a situation that can anticipate students' learning obstacles in algebraic form material and facilitate students' thinking process. Situations are created using exciting pictures and stories to motivate student learning. The results show that the situations that have been created make it easier for students to group similar and dissimilar terms and can operate the algebraic form easily and algorithmically. The students also can interpret the elements of the algebraic form along with addition and subtraction operations in the algebraic form based on the understanding of each student.