This study investigated the impact of Student Team Achievement Divisions (STAD) and Group Investigation (GI), which are two techniques of Cooperative Learning, on students' reading comprehension achievement of English as a Foreign Language (EFL). After administering an English Language Proficiency test (Fowler and Coe, 1976), 90 homogeneous pre-intermediate female college students were selected, and they were randomly assigned to three groups: two experimental and one control. The experimental groups (A and B) received instruction according to STAD and GI techniques respectively whereas the control group was instructed via the Conventional Instruction (CI) technique which followed an individualistic instructional approach based on the exercises in their regular textbook. A post-test was administered, and its results were analyzed through a one-way ANOVA and post hoc Scheffe statistics. The results revealed that STAD is a more effective technique in improving EFL reading comprehension achievement whereas GI and CI did not enhance reading comprehension significantly. Team rewards, as one of the central concepts of STAD, may have a strong impact on learners' performance in reading comprehension. (Contains 6 tables.)