This study examined the impact of cooperative performance on cloze tests on the development of vocabulary knowledge. 70 English language learners were divided into experimental and control groups. The experimental group completed cloze tests cooperatively in small groups, while the control group studied the same passages individually. Both groups took a pre-test and post-test of vocabulary knowledge. The results showed no significant difference between the groups on the pre-test, but the experimental group performed significantly better on the post-test, indicating that cooperative performance on cloze tests improved vocabulary learning. The researchers concluded cooperative learning is effective for vocabulary development as it allows students to learn from each other and receive more input.