Abstrak
One of the essential elements in learning English is vocabulary development. Without a sufficient vocabulary, language proficiency is hindered, and effective communication becomes impossible. Therefore, engaging teaching media, such as Duolingo, is needed. This study aims to determine the significant impact of using the Duolingo smartphone application on the vocabulary mastery of seventh-grade students, specifically focusing on verbs and nouns. The research method employed was pre-experimental. The population of this study consists of seventh-grade students at SMP Negeri 7 Tarakan, with a sample size of 32 students from class VII-4. The research instrument used was a written test in the form of a pre-test and post-test. The data were analyzed using a t-test, and processed with the help of SPSS version 22.0. The results of the data analysis showed that the average pre-test score was 49.84, while the average post-test score was 78.75. The t-test results yielded a value of 0.000, less than 0.05, indicating that the alternative hypothesis (Ha) is accepted, and the null hypothesis (HO) is rejected. Therefore, it can be concluded that teaching vocabulary using Duolingo is proven to be effective in improving the vocabulary mastery of seventh-grade students at SMP Negeri 7 Tarakan.