The phonological loop of the working memory system plays a key role in language learning. This study examined the trajectories between two dual-language learner groups (English Learners [ELs] and Spanish Learners [SLs]) on phonological loop measures in L1 and L2. At Grade 1, children completed a battery of vocabulary and cognitive measures and were retested in Grade 3. A series of random effects ANOVAs showed that SLs outperformed ELs on English loop measures, with strong growth in the English loop, but not in Spanish. No significant difference in Spanish loop performance occurred at Grade 3. Considerations for future research and practical implications are discussed.