Introduction: vocabulary development is a key component in English as a Foreign Language (EFL) learning, particularly in writing skills. However, B1-level learners often show limitations in lexical use, affecting coherence and accuracy in written production. Objective: to analyze the impact of differentiated instruction on vocabulary use and writing performance in B1-level EFL students. Methodology: a quantitative quasi-experimental pretest–posttest design with a mixed-methods approach was applied. The sample consisted of 30 B1-level students aged 18 to 35. The intervention lasted 20 hours and included scaffolded writing activities, differentiated tasks, and formative feedback. Data was collected through writing tests, Likert-scale questionnaires, and observation checklists. Results: significant improvements were found in vocabulary range, accuracy, appropriateness, and coherence. Students also reported positive perceptions of differentiated instruction, and high implementation fidelity was observed. Conclusion: differentiated instruction significantly improves vocabulary use and writing quality in B1-level EFL learners, enhancing linguistic development and learner motivation. General Area of Study: Education. Specific area of study: English as a Foreign Language (EFL) teaching / Vocabulary development in writing
Type of study: Original article.