The flipped classroom is a teaching method that combines technology and group collaboration activities. The flipped classroom can be a good approach for this teaching method because it encourages students' interest in learning. This study aims to find the difference in effectiveness between written and video-based materials for a flipped classroom among first-year students in SMP Taman Siswa Turen, Indonesia. It implemented a quantitative research model that comprises two classes, one was the experimental group and the other the control group. The experimental class was given video-based materials, while the control class was given written-based materials. The data collection in this research used a pretest and a posttest to track the difference in the scores at the beginning and the end of the class. Interestingly, this study reveals that the experimental class had an increased score, from 58.52 in the pretest to 78.33 in the posttest. On the other hand, the control group achieved 54.80 in the pretest and 68.20 in the posttest. Thus, the results show that video-based materials are more effective than written-based materials in a flipped classroom. This finding highlights that English language teachers need to use more video-based materials in flipped classrooms.