Abstract :
The purpose of this research is to describe the comprehension concept of mathematics of SMP student is observe from their basic ability in mathematics. This research is the descriptive qualitative research, the subject of research is consist of three students from the class II SMPK St. YOUSEP NAIKOTEN Kupang. The research begin by determine the subject of research by seeing the semester result before. The three students has a different ability in mathematics as well as their availability also become consideration in choosing the subject, then the researcher give TPM and an interview to the every students. The validity of data is by using the triangulation. The result of research such as: the students have a high ability to understand, identify, and apply the concept of algorithm by telling the meaning and the purpose of the problem. The students could compare, differentiate, and give an example and the example of contra of a right concept in solving problem the summation matter and reduction that in matter. The students could interrogate the concept and principle that is connected in counting after determine the meaning of each symbol in the formula and conclude from the result of their work with their own language regarding the result. Subject that has a high ability could in solving problem the matter appropriate with the steps in indicator. The students that has a medium ability could understand, identify, and by applying the algorithm concept until they could explain the meaning and the purpose of the matter with their own language and to identify what is known. Cannot compare, differentiate, and give an example and the example of contra from a right concept in solving problem the summation and reduction in matter. Cannot substitution the number into the symbol and not capable to interpret the meaning that exist in symbol. Could integrate the concept and principle that is connected to each other by doing counting after find out the formula and substitute the number into the formula and conclude the result of their work with their own language regarding the result of their work. The subject that has a low ability could understand, identify and apply the concept algorithm could tell the meaning and the purpose of the matter with their own language. Cannot compare, differentiate and give an example and the example of contra from a right concept in solving problem the matter. And cannot apply the concept in solving problem the matter is not capable use the formula in solving problem the matter and not capable to explain the meaning of the symbol in formula. Not capable to integrate the concept and principle that is connected, in substitute the meaning of the formula the subject is confused until the subject correct in counting but wrong in answer that is meant and conclude the result of work with their own language regarding their work.