<![CDATA[The pre-experiment study with one group pretest-posttest design had been done in the 10th-4 grade at SMAN 7 Bandar Lampung. This study was aimed to describe the practicality, effectiveness, and effect size of SiMaYang type II learning model to improve mental model and concept mastery on chemical bonding topic. The practicality was determined from implementation of lesson plan and students' responses to the implemention of learning. The effectiveness was determined by the activity of students during the learning, the ability of teacher in managing the learning, and improvement of students mental model and concept mastery. The effect size was determined by t test and effect size test. Results showed that the practicality and the effectiveness of SiMaYang type II were categorized on high, and the effect size of this learning model had a big criteria.Metode pre-eksperimen dengan One Group Pretest-Posttest Design telah dilakukan di kelas X4 SMAN 7 Bandar Lampung. Penelitian ini bertujuan untuk mendeskripsikan kepraktisan, keefektivan, dan ukuran pengaruh model pembelajaran SiMaYang tipe II untuk meningkatkan model mental dan penguasaan konsep siswa pada materi ikatan kimia. Kepraktisan ditentukan dari keterlaksanaan RPP dan respon siswa terhadap pelaksanaan pembelajaran. Keefektivan ditentukan dari aktivitas siswa selama pembelajaran berlangsung, kemampuan guru dalam mengelola pembelajaran, ketercapaian dalam peningkatan model mental dan penguasaan konsep siswa. Ukuran pengaruh ditentukan dengan uji t dan uji effect size. Hasil penelitian menunjukkan bahwa kepraktisan dan keefektivan Model SiMaYang tipe II berkategori tinggi, dan ukuran pengaruh dalam pembelajaran ini memiliki kriteria yang besar.Kata kunci: model mental, penguasaan konsep, SiMaYang tipe II, ukuran pengaruh]]>
