Jurnal Inpafi Vol. 2, No. 3, Agustus 2014 THE EFFECT OF GUIDED DISCOVERY LEARNING MODEL ON THE STUDENT’S ACHIEVEMENT IN PHYSICS OF VII GRADE IN SMP N 1 TEBING TINGGI ACADEMIC YEAR 2013/2014 Fitriah Andriani Rambe and Ridwan Abd. Sani zyxwvutsrqponmlkjihgfedcbaZYXWVUT Physics Bilingual Education Study Program Faculty of Mathematics and Natural Science State University of Medan rambe.fitriah @gmail.com zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIH ABSTRACT The objective of this research is to know the effect of using Guided Discovery learning model on the students’ achievement in physics especially in temperature topic at VII Grade SMP N 1 Tebing Tinggi. The research method is quasi experiment. The populations are all of VII grade students in semester II that consist of 9 classes SMP N 1 Tebing Tinggi. The samples of this research are two classes and consist of 70 students, 34 students from experiment class and 36 students from control class and define by random sampling. Data shows that pre test mean value of experiment class is 42.06 and control class is 40.3. Post test mean value of experiment class is 70 and control class is 65.28. The data distribution of both sample are normal and homogenous. The criteria for hypothesis test is: H0 is accepted if -ttable < t cou nt < ttable and H0 is rejected if t cou nt has another score, where t ta ble obtained from list oft distribution. Research result shows that t-test for concept mastery using a = 0.05, obtained t cou nt = 0.507, where ttable = 1.99. It can be concluded that the experiment class and control class have same ability. The criteria for post test analysis is : Ha is accepted if tcount > ttable and Ha is rejected if t cou nt has another score. Based on research data for a = 0.05, obtained t cou nt = 1.73, where ttable = 1.67. So, there is effect of Guided Discovery Learning Model on the Student’s Achievement in Temperature Topic at VII Grade in SMP N 1 Tebing Tinggi Academic Year 2013/2014. Based on observation using observation sheet of student activity, it can be concluded that the students in experiment class are more active than control class. Key word: Guided Discovery, student’s achievement, physics INTRODUCTION Gagne in Sridevi (2008) state that science is what the scientist does. It is a process by which we increase and refine our understanding and of the universe through continuous observation, experiment, application and verification. Sciences is the body of knowledge, a way of thinking, a way of investigation, and a way of experimentation in the pursuit of exploring the nature (Sridevi, 2008:5). One of science branch is physics, which is study about phenomenon of nature. Learning physics must involve students in science process, inquiry and analysis of contents. According to Gagne (Rao, 2008:21) in science learning process needs to do what scientist do. Scientists do observe, and classify and measure, and infer, and 89