The literacy instruction that adolescent emergent bilingual (EB) students currently receive is insufficient to improve their writing proficiency (Graham et al., 2021; National Center for Education Statistics, 2012). To promote improvements in EBs' writing, evidence-based practices that are culturally and linguistically responsive must be provided not only in English language arts classes but across content areas at the Tier I level (Baker et al., 2014; Linan-Thompson et al., 2018). The purpose of this dissertation study was to (a) examine the effects of a set of social studies-embedded integrated literacy instructional practices and materials that were modified for EBs (i.e., CSEL PACT) on the total words written and writing quality produced by EBs in Grade 11 as measured by an informational writing prompt, and (b) determine the extent to which pretest vocabulary, social studies content knowledge, and reading comprehension skills predicted EBs' total words written and writing quality. A secondary analysis of data was conducted using a subset of data collected as part of a larger randomized controlled trial. EBs were randomly assigned to a treatment condition (n = 98) in which two units of CSEL PACT were taught consecutively or a business-as-usual condition (n = 59) in which they received their typical U.S. History instruction. Results of mixed effects models in which participants were nested within teachers yielded small, nonsignificant (p > 0.05) effects of CSEL PACT instruction on EBs' total words written (g = 0.05) and writing quality (g = 0.07). Additionally, pretest vocabulary predicted (p < 0.05) total words written and writing quality was predicted by pretest reading comprehension and fixed effects of teachers. The small, nonsignificant effect sizes related to CSEL PACT instruction on adolescent EBs' writing skills correspond to findings in previous research (De La Paz et al., 2017; van Drie et al., 2015). Moreover, the significance of reading comprehension skills as a predictor of writing quality matches prior research and theory (Kim et al., 2022). Further investigation into how the role of vocabulary differs in predicting total words written between EBs and non-EBs is needed. [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/en-US/products/dissertations/individuals.shtml.]