This study examined the effectiveness of a vocabulary-building intervention in improving the reading comprehension of Grade 5 and Grade 6 learners in a multigrade classroom at Upper New Visayas Elementary School. Anchored on the premise that vocabulary knowledge is fundamental to comprehension, the study aimed to enhance learners’ word knowledge and overall understanding of texts through structured reading activities. A quasi-experimental research design was employed, involving twelve (12) learners over a four-week intervention period. Data were collected using validated pre-test and post-test instruments to measure changes in reading comprehension performance. Descriptive and comparative analyses were utilized to determine the impact of the intervention. Results revealed a significant improvement in learners’ post-test scores compared to their pre-test performance, indicating that the vocabulary-building intervention effectively enhanced reading comprehension. The findings further suggest that explicit and systematic vocabulary instruction, when integrated into reading lessons, can address learning gaps and support literacy development in multigrade classrooms. The study concludes that vocabulary-focused interventions are essential in improving comprehension outcomes among diverse learners. It recommends the sustained implementation of structured vocabulary instruction and the development of similar intervention programs to strengthen literacy skills in multigrade educational settings.