The study focused on five elementary Mandarin-speaking students' development as writers over a two-year period in US classrooms. Mandarin speakers who came to the US in 2nd, 3rd, or 4th grades demonstrated some language loss in their Chinese writing. We found differences in terms of sentence complexity, character complexity, rhetorical features, and voice in students' writing between Year 1 and Year 2. Students' native language loss was mitigated by their initial writing competence, support at home, and opportunities to write in Chinese at school. Four of the five students' English writing made dramatic improvements in grammar and punctuation, sentence complexity, rhetorical style and voice over the two years. The fifth student, whose writing did not improve, had few opportunities to write in his new school setting. Our findings suggest that the amount and quality of writing opportunities in each language affect students' writing development.