This type of research is development research. The goal is to describe the development process, producing a good learning tool by using cooperative learning type think pair-square based problem solving on cube and block material in class VIII, and describe the effectiveness of learning tools to improve students' creative thinking. The cooperative learning type think pair-square based problem solving makes students more active, during group discussions or when confirming answers to other groups. The subject of this research is the students of class VIII. This research design uses a model developed by Kemp (2011). Learning tools developed in the form of: (1) Learning Implementation Plan, (2) Student Worksheet, and (3) Test Results Learning. Based on the results of descriptive analysis at the trial and in the implementation stage, it is found that cooperative learning type think pair square is problem solving effective to teach the material of cube and beam in class VIII and to improve students' creative thinking ability. This conclusion is based on the ability of teachers in managing good learning, students are active during the learning process, students give positive responses to learning, and mastery learning is classically met.

Keywords: Development, Lesson Plan, Think Pair Square, Problem Solving, Creative Thinking.