The Effectiveness of the Duolingo Platform in Vocabulary Retention and EFL Young Learners’ Attitudes: Evidence from a Private English Center in Vietnam

This article investigates the effectiveness of Duolingo in supporting vocabulary retention among young EFL learners and examines their attitudes toward its use. Employing a sequential explanatory mixed-methods design with a quasi-experimental pre-test/ post-test control group framework, the study was conducted over a 12-week intervention period with 60 learners aged 10 to 11 (CEFR Level A2) at a private English center in Ho Chi Minh City, Vietnam. The experimental group (n = 30) used Duolingo as a supplementary after-school vocabulary tool for approximately 30 minutes per day while the control group (n = 30) received conventional classroom-based instruction only. Quantitative data were collected through researcher-designed parallel-form vocabulary tests and a 25-item Likert-scale questionnaire grounded in the Affective-Behavioral-Cognitive (ABC) attitude model. Qualitative data were gathered through semi-structured interviews with ten selected participants. Paired-samples t-tests revealed that the experimental group achieved a statistically significant mean gain of 0.97 points (t = -13.760, p < .001), approximately double that of the control group (0.50 points; t = -6.412, p < .001), despite equivalent baselines. Questionnaire findings indicated strongly positive attitudes across all three ABC dimensions, with particularly high agreement on enjoyment (90%), motivation (88%) and vocabulary transfer to communicative contexts (93.6%). Interview data corroborated these findings with experimental group learners describing spaced repetition, multimodal input and gamified rewards as key factors supporting retention and engagement. These findings suggest that Duolingo, when implemented as a structured and monitored supplementary tool, can meaningfully enhance vocabulary retention and foster positive learning attitudes among young EFL learners.