The study aims to assess the significance of the English grammar test application for secondary-level students to improve their English language grammar skills. Using an appropriate smartphone application for teaching and learning ESL grammar skills is a challenge that must be considered. On the other hand, other associated challenges, such as internet connection, suitable ESL teaching pedagogy, learners' socio-cultural and socio-economic background, and low level of motivation among ESL learners, need a viable solution. Through mixed method techniques, pre-tests and post-tests were conducted. In both phases of the study, a purposeful sampling technique was used and the assigned teacher and a total of ten students were selected for filling in a questionnaire after the post-test. The data collected from the pre-test and post-test were analyzed through charts and tables, whereas the questionnaires were analyzed through QDA Miner and Word Stat. The study employed Skinner's learning theory of Behaviorism (1976) to practice stimulus, response, and reinforcement techniques. The findings concluded that although the students faced learning constraints, the teacher and the students positively responded to the English grammar test application. The study can be useful for ESL /EFL students in various contexts.