This study aims to assess the overall impact of vocabulary development interventions on cognitive vocabulary outcomes. To achieve this, 43 theses on vocabulary teaching, each involving a specific intervention, were analyzed using meta-analysis. The findings from the meta-analysis, based on the random effects model, indicated that the average effect of vocabulary development interventions on vocabulary outcomes was 1.179. The results demonstrate that interventions designed to enhance vocabulary are significantly more effective than traditional teaching methods in improving students' vocabulary. Furthermore, subgroup and meta-regression analyses revealed that none of the five moderators (pilot study, retention test, method of vocabulary selection, vocabulary outcome [dependent variable], and number of vocabulary items taught) had a significant effect on explaining the heterogeneity in effect sizes. However, the meta-regression results based on the random effects model indicated that the third model, which attempted to explain the variance in effect sizes through sample size and the number of vocabulary items taught, was significant. This model accounted for 44.7% of the variance between studies, explained by the sample size and the number of vocabulary items taught.