Co-operative learning is defined as students working together to "attain groups goals that cannot be obtained by working alone or competitively." The main purpose of co-operative learning is to actively involve students in the learning process, a level of student empowerment which is not possible in a lecture format. The present study found out the effectiveness of co-operative learning in mathematics learning among the eighth standard students of Tirunelveli district. Two equivalent group experimental-designs are employed for this study. The investigator has selected 40 students studying VIII standard in High School, Tirunelveli Educational District. According to the scoring of pre-test, 20 students were chosen as control group and 20 students were chosen as experimental group in a cluster sampling techniques. Finally the investigator concludes that; (a) There was significant difference between control and experimental group students in their gain scores. That is the experimental group student is better than control group students in their gain scores. (b)There was significant difference between control and experimental group students in their gain scores for attainment of the knowledge, understanding, and application objectives.