English learner (EL) children (i.e., children learning English as a second language) constitute one of the fastest growing, yet disproportionately underachieving, segments of the U.S. public-school population. A main difficulty that ELs face at school is learning English and content-area knowledge in tandem. Low levels of English proficiency may limit ELs' abilities to benefit from content instruction in English or to demonstrate knowledge and skills on mainstream academic assessments (Cook, Linquanti, Chinen, & Jung, 2012). This study investigates the time it takes for EL children to attain English proficiency and factors that affect the time by drawing on longitudinal EL data from Michigan. Socio-demographic and English-proficiency assessment data were requested from the Michigan Education Research Institute (MERI) on six cohorts of students who entered Michigan public schools in kindergarten as ELs in 2013-2014 through 2018-2019. All students were followed for up to six years from kindergarten through fifth grade. Discrete-time survival analysis was used to estimate the time that ELs took to attain proficiency as measured by Michigan's state English language proficiency assessment (i.e., ACCESS for ELLs) and to explore the relationship between time to proficiency and six factors of interests: (a) primary disability type, (b) primary home language, (c) poverty status, (d) home English use, (e) instructional programming, and (f) retention. Findings showed that half of ELs who entered Michigan public schools in kindergarten attained proficiency in five years, with writing being the largest barrier to proficiency for those students. Findings of this study further indicated ELs' time to proficiency was significantly related to their sociodemographic and educational backgrounds. Specifically, ELs with disabilities, ELs speaking some particular home languages (e.g., Arabic, AfroAisatic, and Spanish), and ELs who ever lived in poverty were less likely to attain proficiency than their peers who did not have those backgrounds. In addition, ELs who received partial instruction in their home language (L1) and ELs who never used English at home were equally likely, and in some cases slightly more likely, to attain proficiency as compared with their peers who were immersed full-time in an English-only environment at school and at home. Lastly, students who were ever retained in grade were less likely to attain proficiency than their peers who were never retained in upper elementary grades despite short-term gains associated with retention in early elementary grades. Implications of these findings point to the importance of improving current accountability systems to reflect the diversity of the EL population, supporting L1 maintenance in the home and school contexts, monitoring the effect of retention on ELs, and providing better writing instruction for ELs. [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.]