This study aims to produce science learning tools that are valid, practical, and effective which consists of syllabus, lesson plan, teaching material, student activity sheets, and test sheets to improve the critical thinking skills of elementary students. This research was carried out using the 4-D model of adaptation Ibrahim, M., which is define, design, developing, disseminate and tested in class V of Jiken Elementary School, Kedondong I Elementary School, Sudimoro Elementary School, school year 2019/2020 with One-Group Pretest-Posttest Design. Data analysis techniques used are quantitative and qualitative descriptive. The results shows: 1) valid, according to the validity of the three validators with valid categories, 2) practical, in accordance with the level of observers seen from the activity of students increasing at each meeting and implementation of RPP, 3) effective, seen from appearing significantly different from the pretest and posttest test students' critical thinking and positive student responses. Based on the results of data analysis, it can be concluded that the development of science learning tools oriented in guided inquiry is valid, practical, and effective for improving critical thinking skills of elementary students.

Keywords : Development of Learning Tools, Guided Inquiry, Critical Thinking Skills