This quasi-experimental study aimed to investigate the effect of flipped classroom strategy (FCS) on tenth graders' vocabulary achievement and to measure students' motivation towards learning English as a result of using this strategy. This study also sought to explore the challenges that students face while learning by the FCS. A total of forty-eight students participated in the study: twenty-four students formed the experimental group and were taught via the FCS and twenty-four students were taught the same vocabulary using conventional teaching strategies as a control group. During the intervention, students in the experimental group practiced the core vocabulary using different materials: video clips (fill in vocabulary logs), PDF files and group discussions via a WhatsApp group before carrying out face-to-face activities in the classroom. During the classroom time, the students engaged in activities with the practice materials individually, in pairs and in groups. As a main tool for the study, the researcher used an achievement test of four questions (20 items) designed and validated to be used as a pre- and post-test. As a pre-test, the achievement test was intended to prove the groups' equivalence. Then, it was used as a post- test to measure any possible differences in Academic achievement between the two groups. In addition, the researcher used a motivation questionnaire (pre & post) to determine the students' motivation for English language learning for both groups. The findings indicated that the experimental group outperformed the control group in the vocabulary test and that they had high motivation towards learning English as a result of using the FCS. In addition, the study also pointed out some of the challenges of learning via FCS such as; connectivity issues, technical problems, time, workload and lack of groups' cooperation were the main challenges, whereas availability of devices, lack of language skills and boredom with long PDF readings were considered minor challenges. In light of these findings, implications and recommendations for further research are presented.