This research focused on development of group investigation cooperative learning model. Therefore, this research aims to describe result and process of the learning model development and evaluates effectiveness of the group investigation (GI) type cooperative learning on rectangular material.

The learning model research and development procedure referred to “Designing Effective Instruction†by J.E Kemp, with pilot test using one group pretest-posttest design. Research subject consisted of 31 students from 7^th Grade of Junior High School. Research result demonstrated that the learning model fulfilled valid, practical and effective criteria. The developed learning model covered lesson plan, student activity sheets and study exam. Effectiveness of the group investigation cooperative learning indicated effective outcome because fulfilling the criteria of good category on teacher’s capability in learning process, class classical completion achieved 83,33% and the students showed positive response.