This study aims to create an inquiry physics lesson plan (valid, practical, and effective) which is used to train the metacognitive skills of the students of Muhammadiyah 2 Senior High School in Sidoarjo. The improvement of lesson plan used the ADDIE model and tested in the XI MIPA class of SMA Muhammadiyah 2 Sidoarjo Muhammadiyah 2 Senior High School in Sidoarjo on the first semester of the academic year 2017/2018 with One-Group Pretest-Posttest Design. The Data collection used validation, observation, tests, and questionnaires. The Data analysis techniques used quantitative descriptive analysis. The results of this study indicate: 1) The development of lesson plans ,which is improved, are valid; 2) The learning process based on the improvement of lesson plan and implemted to the students run well; and 3) The effectiveness of lesson plan are: (a) Improvement of student learning outcomes aspects of knowledge seen from n-gain are in high category (b) Student responses to lesson plan and the implementation of learning are very positive (c) The results of metacognitive skills of students who are trained are very well. It was concluded that the inquiry learning model which is improved here was feasible (valid, practical, and effective) and was used to improve the metacognitive skills of the students of Muhammadiyah 2 Senior High School in Sidoarjo.

Keywords : The Improvement of Lesson Plan, Inquiry Learning Model, Metacognitive Skills.