This study examined the effects of two kindergarten literacy interventions on Grade 1 spelling outcomes among monolingual Spanish-speaking kindergarteners in low socioeconomic schools in Argentina. One intervention targeted phonological awareness (PA) and basic phonics, while the other was a multicomponent intervention integrating PA, morphological awareness (MA), and vocabulary instruction. A control group followed the standard kindergarten curriculum without explicit literacy instruction. The interventions were delivered over three months by classroom teachers. Repeated measures ANOVAs showed that both intervention groups outperformed the control group on spelling at posttest, with large effect sizes. Vocabulary outcomes were significantly higher in the multicomponent group compared to both the control and PA-only groups. No between-group differences were observed in phonological awareness gains, although all groups improved over time. The results suggest that both PA-focused and multicomponent instruction can enhance early spelling skills in transparent orthographies such as Spanish, with the multicomponent approach offering additional benefits for vocabulary development. These findings support the integration of MA and vocabulary into early literacy curricula and underscore the potential of teacher-delivered interventions to promote foundational literacy skills in under-resourced settings.