This study explored the science learning experiences of elementary English Language Learners (ELLs) in a fourth-grade mainstream science classroom in an urban setting. Informed by ethnographic research and case study design, this study interrogated the celebrated and marginalized practices within common classroom procedures and what science-related identities the focal ELLs developed within classroom interactions through the lens of identity as position. Additionally, this study examined how the focal ELLs perceived themselves as science learners and how they affiliated with what scientists do and school science. Data collection lasted for two months and included video recordings of science instruction and classroom interactions, interviews with the focal ELLs, and students' artifacts. Findings revealed that "doing science" in this fourth-grade science classroom was narrowly defined, as the celebrated practices involved mainly following the classroom behavioral codes and telling the right answer to the teacher's questions. Findings also showed that the three focal ELLs complied with the celebrated practices to various degrees and were positioned marginally or negatively by the teacher and peers. The marginal and negative positioning affected the focal ELLs' opportunities to engage meaningfully in classroom learning activities. Finally, findings regarding the focal ELLs' perceptions of themselves as science learners showed the various ways in which they used their experiences inside and outside the classroom to construct their understanding of and relations with scientists and the science subject. This study provided implications for student science identity research and practice for supporting ELLs in the mainstream science classroom. [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.]