This thesis attempts to measure the impact of a learning-by-teaching (LBT) strategy on the improvement of EFL learners' vocabulary and their participation in the classroom. To this end, a quantitative study was conducted on 50 students who were randomly divided into 2 groups (control group and experimental group), 25 members each. Specifically, the study evaluated the idea that students being taught under the LBT will achieve higher scores on the post-test of vocabulary compared to the pre-test, and that there will be a statistically significant difference at the 0.05 midpoint of the post-test of the experimental group and control group. It was also theorized that the experimental group would score significantly higher than the control group on the learning engagement questionnaire, administered at the end of the course. Various activities were used with the experimental group, while the control group were exposed to the traditional method. A homogeneity test was performed for both groups at the start of the experiment to ensure that they had the same language background. Finally, a post-test questionnaire for vocabulary and learning engagement (behavioral engagement, cognitive engagement, and emotional engagement) was assigned to both groups to determine if LBT had a positive impact on vocabulary enhancement and learning engagement. The study has revealed that: 1) the LBT enhances students’ vocabulary knowledge; 2) the LBT will significantly persuade learners to have a more active participation and engagement in classes. In light of these results, the following recommendations were made: 1) that LBT could be considered as a way of motivation and learning engagement. 2) That through LBT, students can overcome the problem of learning vocabulary in a joyful way.
