IMPROVEMENT THE CONCEPTUAL UNDERSTANDING ABILITY OF STUDENT THROUGH PROBLEM BASED LEARNING (PBL) MODEL ON TOPIC POLYHEDRAL (CUBE AND RECTANGULAR PRISM) IN MTS. AL-WASHLIYAH TEMBUNG ACADEMIC YEAR 2012/2013

The aim of this research is to improve the conceptual understanding ability of student through problem based learning model was done in Mts. Al-Washliyah Tembung. The type of this research is Classroom Action Research. The research has done respect to the student of VIII-1 in number 40 students.
Instrument used to collect the data is conceptual understanding mathematics test and observation sheet. These researches consist of two cycles and the end of every cycle given conceptual understanding mathematics test. Before given, at the first test must be validity. Validity test done is contents validity where expert as validator.
The result in this research has shown that learning by problem based learning model can improve the conceptual understanding mathematics. From initial test that given to student said that student has good ability in prerequisite material. It indicate from the average value of initial test of 40 student is 82.50. This case shown from the result before treatment, in first conceptual understanding test I of 40 students there are 18 students (45%) gained the score  70 with the average class is 48.25.
After given treatment so the students do the conceptual understanding test II of 40 students there are 35 students (87.5%) gained the score  70 with the average class is 82.25. The observation sheet get average score 2.735 in cycle 1, its in good category. In cycle 2 get average score 3.365, it indicate teacher is very good category in implement problem based learning in classroom.
From the result of research can conclude that by implementation problem based learning model can improve the conceptual understanding of student. Mathematics teacher of Mts. Al-Washliyah Tembung suggested can implement problem based learning model in improving conceptual understanding of student. To students suggested more active to found the concept of mathematics.