The effectiveness of Cooperative Learning Approach in Improving the Students’ Activi­ties and Learning Achievement. This classroom action research (CAR) was aimed at improving the students’ learning achievement through the application of Cooperative Learning Approach. There were 26 students involved in the study which took place in the academic year of 2007/2008. Observations were conducted to collect relevant data on students’ and lecturer’s activities. The students’ achievement was measured using a test. Computation in the forms of percentage and average score was carried out to show the results of the data analysis. The results demonstrate that 1) the students’ scientific attitude in Cycle I was quantified as 60.69%, in Cycle II 71.16%, in Cycle III 80.77%,  2) the lecturer’s teaching activities were getting better as the cycles progressed, and 3) the students’ achievement in Cycle I was 5.92, in Cycle II 6.71, and in Cycle III 7.62. The results show that the application of Cooperative Learn­ing Approach can improve the quality of students’ learning activities and the students’ learning achieve­ment.