The flipped classroom is a teaching approach that can afford additional face-to-face communication with students in the classroom. Although there are some studies that have already investigated the flipped classroom in general, few studies have investigated critical thinking and performance in learning grammar, in particular. The design of the study was a quasi-experimental research. This research was performed within an English class for six weeks in 2020. Three hundred and sixty English learners were chosen through multistage cluster sampling from two different institutions within the range of 13-19 who were studying at intermediate and upper-intermediate levels. Among fifty grammar videos, eight grammar contents based on content validity index (CVI) and content validity ratio(CVR) were selected. Questionnaires were EPT (English performance tests) and CT (critical thinking). The experimental group was educated with the flipped classroom model whereas the courses were performed based on the present syllabus in the control group. It was realized that there was no substantial discrepancy between the pre-test and post-test the scores of the control group while there was a significant difference between the pre-test and post-test scores of the experimental group. Teachers can be proposed to manipulate the flipped classroom model to boost learners’ critical thinking and performance.