Improving Students’ Vocabulary By Using Duolingo at SMK Veteran 1 Sukoharjo: A Classroom Action Research of the XI BC 1 of SMK Veteran 1 Sukoharjo in the Academic Year 2025/2026

Abstract

This article discusses the results of a Classroom Action Research (CAR) conducted to improve students' vocabulary mastery through the use of the Duolingo app. The participants were 37 students of class XI BC 1 at SMK Veteran 1 Sukoharjo in the 2025/2026 academic year. The research was conducted in two cycles following the Classroom Action Research model, consisting of planning, action, observation, and reflection. Data were collected through vocabulary tests, observation, interviews, and a student response questionnaire. Quantitative data were analyzed using mean scores and mastery percentages, while qualitative data were used to support the interpretation of the findings. The results show a significant improvement in students’ vocabulary mastery, as indicated by the increase in the mean score from 64.6 in the pre-test to 73.7 in the post-test of Cycle I and 80.3 in the post-test of Cycle II. The mastery percentage also increased from 35.1% in the pre-test to 54% in Cycle I and 75.6% in Cycle II. Questionnaire results further indicate that students responded positively to the use of Duolingo, with response percentages ranging from 77.02% to 87.16%. These findings confirm that Duolingo can effectively support vocabulary learning when implemented as a supplementary medium in classroom instruction.