In recent years, there has been increasing interest in language learners' beliefs in second language acquisition (SLA). Nonetheless, few studies to date have investigated the extent to which learners' beliefs develop, and the factors that contribute to this development have not been examined seriously. Employing a naturalistic inquiry, this longitudinal study investigates the development of five Chinese immigrant learners' beliefs in a new learning context, New Zealand. Using a multi-case study design, this study identified three major changes in the learners' beliefs and the factors that led to these changes. Cognitive dissonance was the first and the most important factor. Another factor stemmed from the teaching methods the learners were exposed to. Finally, the learners' own language progress, their positive learning experiences, and the encouragement from their teachers also contributed to the change in their self-efficacy beliefs. The study reveals that apart from these three noticeable changes, the majority of the learners' beliefs remained relatively stable over the observed period, which suggests a duality of their beliefs. The findings of this study have important theoretical and practical implications, particularly in terms of advancing our understanding of the nature of learner beliefs in SLA.