This design-based research study explored how collaborative writing activities can be used in support of ELLs' writing development in the context of a culturally and linguistically diverse first-grade classroom. Using qualitative methods, I examined two focal ELL students' participation across four iterations of collaborative writing activities, analyzing their interactions and collaboratively written texts. Additionally, I explored the context in which each iteration of collaborative writing activities was implemented, focusing specifically on the teaching and learning activities surrounding the collaborative activities and the interactions between the teacher and her students. By analyzing audio recordings, field notes, classroom artifacts, students' written texts, teacher interviews, and debriefing notes, this study aimed to answer the following three research questions: (1) What is the nature of first-grade students' (ELLs and their partners/group members) interactions when participating in collaborative writing activities? (2) How do the two focal ELL students' written texts compare across the collaborative writing activities? (3) In what ways can collaborative writing activities be scaffolded to support ELLs' writing development in a diverse first-grade classroom? The findings from this study indicated that the two focal ELL students demonstrated dynamic patterns of interaction when working with their peers throughout the four iterations of collaborative writing. These patterns, characterized by unique language features and scaffolding occurrences, were identified as collaborative, collective, dominant/passive, and expert/novices. The evaluation of students' writing revealed that their collaboratively produced texts were varied across the writing activities, as they were tasked with producing texts from four different genres. In some instances, the students' texts revealed their clear understanding of the genre, including its purpose and stages, as well as their ability to control and implement different language features. However, in other cases, their texts showed that they needed further instruction or revision in specific areas. Findings also revealed specific ways in which the collaborative writing activities were scaffolded to support ELLs' writing development in this first grade classroom. Before the writing activities, the teacher prepared students to write collaboratively and utilized planned scaffolds to design and structure the different activities. During the collaborative writing activities, the teacher employed interactional scaffolds and facilitated the revision process to support the ELL students in producing texts that aligned with the writing goals. After the collaborative writing activities were completed, the teacher encouraged students to share their final product and invited them to participate in a discussion to debrief about the writing activities. Ultimately, this study contributed to the field of second language writing by (a) highlighting the rich and dynamic patterns of interaction that can arise when ELLs have the opportunity to participate in collaborative writing activities, (b) showcasing the high quality texts that ELL students can produce when writing collaboratively, and (c) identifying effective scaffolding practices as they relate to implementing collaborative writing activities in culturally and linguistically diverse classrooms. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]