The Effect of Problem Based Learning (PBL) Method on Students’ Critical Thinking Ability in Fifth Grade Science Learning in Elementary Schools

This research was conducted in elementary schools to determine the effect of the PBL method on the critical thinking skills of fifth grade elementary school students using the PBL method in science subjects. In this study with a population consisting of 59 fifth grade elementary school students, the sample in this study was divided into 2 classes. A few of them; First, the experimental class. Second, the control class. The sampling technique used is a non-probability sampling technique. The design of this study used a posttest only design. In this study, the data collection process used 10 essay questions, the validity test used the product moment formula as many as 10 essay questions with the results of 8 valid questions and 2 drop questions. To test the reliability using Cronbach’s alpha. Data analysis using t-test proves that the value of t_count is greater than t_table 3,645 > 2,002, this research can be concluded that “there is the thinking ability of fifth grade elementary school students in science subjects by applying the Problem-based method (PBL) method”.


INTRODUCTION
Critical thinking in students according to (Saputri, 2020) is an activity to encourage students to be in order to have a soul that is steadfast to the establishment, active and always carefully. Then students are able to conclude, analyze and evaluate from a problem that is obtained based on logical thinking. A participant during the learning processed be necessary to have the skills to develop a critical mindset, because then the learning environment in the classroom can be active and fun so that students do not feel bored. Students are able to solve problems and analyze and evaluate the problems they are facing in the form of knowledge. Critical thinking is done to make a decision, and evaluate the truth of a statement (Ejin, 2016).
In critical thinking there are activities in it, like solving a problem, then analyzing an assumption to make a decision, and conducting research and solving problems that are being faced. According to (Alimirzaloo & Hashemnezhad, 2016) Basically, critical thinking is an activity that requires high-level thinking in solving a problem and in making decisions. (Tan, 2004) revealed that the challenged is learned that requiresed students to focus on a problem in order to be capbled to solve the problem in the form of a solution. Students develop critical thinking skills, because deeper levels of critical thinking skills are needed to produce appropriate problem solving skills. According to research conducted by (Saeed & Rousta, 2013) by providing students with problem-based activities, students can better influence students' critical thinking ability.
PBL is a problem based method to help students and encourage students to develop in solve a problem by thinking critically to students' dailies, and dare to express their opinions, Thus in solving a problem by students are required to be active in information solicit about the problem, and research from these problem (Lestari & Projosantoso, 2016)(2. In developed students' critical thinking skills to solve problems in elementary schools, namely by used Problem Based Learning as a learning-based method. Thus, students will focus on solve badly complex problems so that students are capbled to find solutions to solve these problems, either individually or in groups (Muslim et al., 2015).
According to (Susilo, 2012) Natural science (IPA) is either of the main subjected in elementary schools in the education curriculum in Indonesia, science or science is one of the subjects that are considered important. Science learning is aching and learning activities in the classroom and only makes students as recipients of information, because teachers still use the lecture method or conventional). Teachers also do not associate learning materials with real problems in everyday life or problems that exist around us, so that in science subjects, students tend to find it difficult to understand on the grounds that the teacher does not support students to play an active roles in expressed opinion (Agustin, 2013).
In this research, researchers have reasons for chooses science subjects, where that selection is because researchers consider that students tend to have difficult understanding these subjects, especially in terms of expressed opinion or idea, and teachers at fifth grade of elementary school West Jakarta had never applied other science subjects. method other than using the lecture method, in this study the researcher will try to apply another learning method, namely by using the PBL method, in this study the researcher chose class V because the class V teacher did not provide opportunities for students to think critically, play an active role in the learning process and able to solve problems in learning science in grade V elementary school, especially with heat and temperature transfer materials.
Based on Ahmad Farisi's research in the journal Elementaria Pendidikan in 2017 with the research title "The effect of problem based learning (PBL) learning models on critical thinking skills in improving student learning outcomes" which has been proven by using PBL in elementary school he describes understanding using the PBL model that succeeded in changing the understanding of students who did not understand the material to understand the material, the material not only listened to the teacher but applied the material in their lives. so that research using PBL can encourage students to play an active role and be able to solve problems in science learning in real life, and be able to express ideas (Farisi et al., 2017).
For this reason, it is expected that teachers can apply methods that make students more active and train students' critical thinking skills in solving problems in real science learning. This can make students understand the material presented by the teacher in a meaningful way, namely through the use of a problem based learning model, which is expected to improve students' critical thinking skills, encourage students to be more active and be able to solve problems systematically with heat transfer material for class V students through In this study, researchers used quantitative experiments with the title the effect of problem based learning(PBL) on students' critical thinking skills in science learning in class V in elementary schools.

METHOD Research Design
This research was using a quantitative research with a quasi experimental type of research, the design of this study uses a post-test design only. O 1 : post-test in the experimental group after participating in learning using the problem based learning(PBL) method O 2 : post-test in the control group after participating in learning using conventional methods. X : the treatment in the experimental group is given learning using the problem based learning(PBL) method -: treatment in the control group is given learning using conventional methods.

Procedure
The steps in the preparation stage are: (1). conducting observations to determine the condition of the school and the science learning process by the teacher at the school., (2). identifying problems based on pre-research results., (3). making learning tools, as follows syllabus, RPP, LKPD, the assessment sheet and make student activities during the learning process., (4). Validate research instruments., 5) Revise research instruments after validating., (6). Conduct test questions in the control class and experimental class.
The stages of implementation in research: (1) carry out learning in accordance with RPP., (2) Provide learning activities using the PBL method., (3) Give final test questions after conducting research to determine students' critical thinking skills in solving a problem in learning science.
This research was conducted in an elementary school, where in the selection processed the researcher observed that school had not used problem based learning as a learning method. Quantitative experiment is a type of research used by researchers with a quasi-experimental method used a pottest only control as a type of design. In this research, the sampled is classified into twos, namely: First, the experimental class. Second, the control class (Sugiyono, 2015). As long as to the learn processed, which consisted of 59 people who were divided into two samples, the researchers used distinct methods. The control class uses conventional as the method, and the experimental class uses problem based learning as the method. The researcher used the normality which was supported by the Lilifors test and the homogeneity test which was supported by the Fisher exact test.
Sampling of data in this study using nonprobability sampling. Before conducting the research, the researcher conducted a validation test first to find out whether the instrument was valid or drop. Researchers used product moment as a validities test and Cronbach's Alpha formula as a reliabilities test. Posttest-only control design is a type of experiment that is used by researchers as a research design, where that design will be realized on two samples, namely the control class and the experimental class. Based on the table 2. the results of the validation calculations, the results of the value for 30 students or n = 30 at a significant level of 0.05%, namely 0.361. The value of the product moment correlation coefficient is compared with the product moment correlation r value with n = 30 at a significant level of 5%, namely 0.361. The conditions for each item that are counted as valid are > Classification of validity test questions of the 10 questions tested there are 8 valid questions and 2 drop questions, in this study the researchers only used 8 questions so as not to burden students.The reliability test was carried out after knowing questions that were already valid. After knowing the valid questions totaling 8 questions, the researcher calculated the instrument reliability test using the alpha Cronbach formula. Reliability serves as a measuring tool that describes the accuracy of the test takers to answer the questions, the instrument is said to be > . After calculating using the Cronbach alpha formula, it is obtained the value of as follows: Based on the table 3. After calculating the results, it is concluded that = 1.020. At r_table at a 0.05. N= 30 is 0.361. = 1.020 > 0.361 So that science subjected that uses students' critical thinking skills can be said to be "reliable" and classified as high relabel and suitable for use as research. Accord to table 4. which has been described above, the two samples used by students in science subjects in this research were the experimental class uses the PBL method which aims to improved students' critical thinking skills and the control class using conventional as a method.

RESULT AND DISCUSSION
In this research, whem is a requirement in determining the normal or abnormal distribution is by used the normalities test. In this research uses the normalities test using Liliefors test at a significant initial of 0.05. H 0 : Data comes from a normally distributed population H 1 : Data comes from population with abnormal distribution.
Accoord to table 5. The normality test for the control class after data processing is Lo = 0.0676 with n = 30 and a significance rate of a = 0.05. Because Lo < Ltable is 0.0676 < 0.1610. So Ho is optained, that the author can conclude that a normally distributed population is used for the sample.
Accord to table 5. Test the normality of the experimental class after data processing, namely Lo = 0.0869 with n = 29 and a significance rate of a = 0.05. Because Lo < Ltable is 0.0869 < 0.2490 . So Ho is optained, that the author can conclude that a normally distributed population is used for the sample. H 0 : The variance of the two sample data is homogeneous H 1 : The variance of the two sample data is not homogeneous Based on the table 6. From the control class and experimental class data obtained = 77,509 and = 68,595 with a significant a = 0.05 with dk in the numerator = 29-1 = 28 and dk in the denominator = 30 -1 = 29. Then a = (0.05,28,29) Ftable = 1.868 Because Fcount is smaller than Ftable, namely =1.130 < 1.868, it can be concluded that Ho is accepted that the variance of the two groups is homogeneous. There is no effect of the problem based learning method on the critical thinking skills of fifth grade students on heat transfer material at an elementary school in West Jakarta. H 1 : There is an effect of the problem based learning method on the critical thinking skills of fifth grade students on heat transfer material at an elementary school in West Jakarta. Based on the table 7. The results of the ttest calculation in table 6 can be seen that uses a significant neural value of a = 0.05 with dk = 59, dk = 59 -2 = 57, so the value of is 2,0002. while is 3.645.then > Ttable which is 3,645 > 2,002. then based on the test criteria Ho is rejected and is accepted. The conclusion in this study is that is accepted, which states that there is an effect of the problem-based learning method on students' critical thinking skills in science learning class V in elementary schools.
This research proves that by applied the problem based learning method can activated the roles of students in solving a problem, where by used that method, students are trained to find solutions to every problem in everyday life. This can be proven by the final results of science learning which were analyzed by researchers regarding the value obtained by each class. the control class got 80,100 acquisition and the experimental class got 86,655 acquisition. Mental development, social development in students, cognitive development in students and the development of science or science. Because every human being grows differently and to grow and develop in critical thinking, because in learning takes place critical thinking in students is very necessary when learning takes place such as reasoning and daring to explain ideas or daring to express an opinion or idea that students have (Susilo, 2012).
From the research results according to Shofiyah Maqbullah, Tati Sumiati, Idat Muqodas. Based on the results of this study, they were: actively participating in solving problems posed by the teacher, students also conducting group experiments, conducting scientific experiments, and conducting individual and group questions and answers. group. In addition, students discuss solutions to analyze and evaluate problems. Students' critical thinking skills have increased very satisfactorily in each cycle by using the Problem Based Learning method (Maqbullah et al., 2018).
Thus the value obtained by the experimental class is superior to that obtained by the control class. This is reinforced by the acquisition of the t-test which shows the value of is greater than (3.645 > 2.002). Experiment class 29 0,0869 0,2490 < Data is normally distributed. Therefore, the PBL method can significantly affect 5th grade students in science subjects related to critical thinking ability.

CONCLUSION
Based on the explanation of the results of this researched, it can be concluded that what was obtained by the fifth grade elementary school students in science subjects with the theme of heat transfer and temperature in the experimental class and the control class. the results of the experimental class scores are superior to the control class. This is based on the fact that research using the Problem Based Model (PBL) in the experimental class states the existence of critical thinking skills in fifth grade students in elementary school in science learning until students in that class are able to think critically with test results that represent the value of is greater than (3,645 > 2,002).