Critical thinking skills are essential for success in life and work, and it is essential that learning strategies enable the development of critical thinking skills from the early years of schooling. The objective of this study is to evaluate the effectiveness of cooperative learning using the RoundTable and Think-Pair-Share methods in the development of critical thinking skills such as observation, inference making, interpretation, analysis, and argumentation, in 4th graders students. The study employed a quasi-experimental design with a pretest and posttest using equivalent experimental and control groups. Results show that the use of cooperative learning, compared to a more traditional teaching methodology, was more effective in developing the critical thinking skills under study.