Abstract :
These research aims to develop study peripheral of cooperative type "Group Investigation" at flat side space similar topic in class student VIII SMP PGRI 01. Study peripheral developed is execution plan of study (RPP), student spread sheet (LKS) and teaching material in the form of student book adapted for by condition of the school that is peripheral applied is RPP and schoolbook. This research is expansion research type with expansion models; peripheral applied is model 4D (Define, Design, Develop, and Disseminate) which do been modified to become 3-D (Define, Design, and Develop). This research test-driving in even semester by 28 March up to 04 Aprils 2011 at Junior High School (SMP) PGRI 01 Dau Class VIII with testing subject 21 students and done by counted 4 times meeting. Instrument applied in this research is validation sheet, interview guidance, and observation sheet and student response inquiry. Result of expansion research of study peripheral of cooperative type group investigation with flat side space similar discussion fundamental at class VIII Junior High School (SMP) PGRI 01 Dau Malang, indicate average of validation of peripheral developed is for execution plan of study (RPP) obtained percentage that is 93%, student spreadsheet (LKS) obtained percentage that is 92%, and teaching material do obtained by percentage that is 91%. For average of percentage overall off from third of peripheral developed the equal to 92% with very competent category (very valid). Average yield percentage of management of teacher in study applies study peripheral of co-operative type group investigation is obtained by percentage equal to 88% with good criterion. For student activity in study applies study peripheral of cooperative type group investigation is obtained by percentage equal to 78% with good category. For student response applies study peripheral of co-operative type group investigation is obtained by percentage average of every aspect is 38,60 hardly agreeing, 38,96 agreeing, 21,90 disagree and 054 hardly disagree.