This multiple case study investigated adolescents' participation patterns and trajectories in an integrated STEM plus digital Literacy (STEM+L) project. The project aims to broaden adolescents' participation in integrated STEM+L practices. In the project, fifth to eighth graders worked in small groups of three to four to create multimodal science fictions. In this study, I explored forms and degrees of students' participation through two theoretical perspectives: disciplinary identity development and community of practice. The former provides a necessary lens for investigating "forms of participation" in three dimensions: attitudes and interests toward disciplinary roles, disciplinary knowledge and practices, recognized by oneself or others as disciplinary experts. The latter allows me to explore degrees of participation in two aspects: the breadth (e.g., time on task) and the depth (e.g., consuming or producing ideas) of participation. The following three research questions guided the study: 1) What are the notable patterns and trajectories of students' "forms of participation" in STEM+L practices through disciplinary role taking? 2) What are the notable patterns and trajectories of students' "degrees of participation" in STEM+L practices in terms of breadth and depth of participation? 3) What is the "relationship" between students' forms of participation and degrees of participation? To answer the research questions, four cases were selected and multiple sources of data were collected, including surveys, semi-structured interviews, student-generated multimodal artifacts, logging data in the iKOS system, video records of group working, and field notes. Specific data sources for the four focal cases varied based upon students' choice of multimodal composing platforms, availability of video and interview data, and relevance of data to each individual case. Our analysis of these data was mainly qualitative in nature, driven by our research questions centered around students' forms and degrees of participation in STEM+L practices. Synthesizing findings from each case suggests that changes in the form and degree of participation, and the relationship between the two, could be due to the following factors: 1) Reflective understanding of the nature of (inter) disciplinary practices and roles; 2) Exposure and experience in composing in multiple modality; 3) The interaction between self and the community; 4) The relation between self and artifacts. This study may inform the field the nature and possible causes of adolescents' forms and degrees of participation. Integrated STEM+L practices mediated by multiple modes can not only offer students flexibility in moving across forms of participation, but also open space for them to demonstrate their expertise as knowledge producers. Important implications were suggested regarding what can be done to facilitate the development of disciplinary identities and the extension of participation in integrated STEM practices. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]