This study explores cross-language and longitudinal patterns in unconventional word segmentation in 25 emerging bilingual students' (Spanish/English) writing from first through third grade. Spanish and English writing samples were collected annually and analyzed for two basic types of unconventional word segmentation: hyposegmentation, in which at least two graphic words are written without conventional spaces, and hypersegmentation, in which blank spaces are deposited within one graphic word. In addition to exploring instances of unconventional segmentation, this article investigates similarities in and differences between such patterns in Spanish and English. In both languages, hyposegmentation was more common, illustrating that children tend to leave fewer blank spaces in their writing than typical writing conventions require. Furthermore, students had more instances of hypersegmentation in their Spanish writing. Findings illustrate the importance of understanding writing development from a bilingual perspective and indicate that teachers in the primary grades must explicitly teach word boundaries and assist children in learning the conventional concept of words and word boundaries.