Due to low English language arts (ELA) state test scores among Hispanic students, district administrators in a Title I identified school district implemented a new literacy policy that included both supplemental education services for Hispanic students (SES-HS) and professional development in cultural and linguistic instructional practices (CLIP) for ELA teachers. But the ELA state test scores for Hispanic students who received the SES-HS and CLIP services had not been studied to see if there was any improvement related to the CLIP-HS training. The purpose of this study was to examine the difference in Hispanic students' ELA scores before and after CLIP-HS PD and SES-HS. Vygotsky's social development theory grounded this study. A convenience sample of 111 Hispanic students who participated in the SES-HS program over a 6-year period (2016-2021) were collected as the students progressed from Grades 7-12. A t test was used to compare the average ELA test scores of each student for the 3 years (2016-2018) before the CLIP-HS PD, and average ELA test scores of the same students for the 3 years after (2019-2021). The results, t(110) = 16.53, p < 0.001, indicated that ELA scores after the CLIP-HS PD was introduced were significantly higher (M = 53.18, SD = 33.89) than before the ELA teacher training. Based on these findings, a recommendation was made for school leaders to offer the CLIP-HS PD for all teachers and to continue the SES-HS initiative. Positive social change accrues when ELA proficiency supports the academic success of students. [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.]