As according to curriculum mount set of education 2006 subject of mathematics of elementary school have been taught a items determine FPB and KPK. Process execution study determine FPB and KPK done simply namely the direct teacher give how way of determining FPB and KPK. The Process done by without there is something that draw for student, so that result of learning the student still less. Pursuant to result to flashback from process of study of mathematics specially at items of FPB and KPK during the time still meet some constraint that is : (1) source learn to base on teacher; (2) belum/tidak put in the way of student to enquire; (3) asking for student to reply question exist in book of packet about taught items (4) less pay attention to student enthusiasm; (5) study only the centre on learn and election of substance teach solely relied on a packet book. At activity of study of activity of teacher experience of improvement from cycle of I and cycle II. At cycle of I of activity of teacher reach 69,6% and cycle of II of activity of teacher reach 89,3%. While activity of student at cycle of I reach 63,8% and cycle of II of activity of student reach 85%. Data of result of tes student at cycle of I reach 63,9% and cycle of II reach 88,9%. the Iesson alloted by sheet of enquette to know respon student. percentage of Enquette reach 90%. From inferential the result that applying model study of co-operative of type of STAD can improve result learn student at items of factor biggest federation and fold of smallest federation. at subject of mathematics of class of V SDN Komplek Kenjeran II Surabaya.