This quantitative, correlational-predictive study examined the predictive relationship of the NWEA's Map Growth projected proficiency report data with students' STAAR scores in the area of mathematics, using archival data from the 2021-2022 school year. The theoretical foundation for this study was provided by Vygotsky's zone of proximal development. Three research questions asked to what extent the NWEA's MAP Growth assessment significantly predicted STAAR Mathematics assessment results for students in third through fifth grades (one research question per grade level). Convenience site selection from one school district in western Texas was followed by random sampling of n = 100 student records per grade level. The final samples for each grade exceeded the minimum sample size of 89 complete student records estimated in G*Power. The results from three simple linear regression analyses showed statistically significant predictive relationships for all three grades: third grade, R[superscript 2] = 0.686, adjusted R[superscript 2] = 0.683, F(1, 98) = 214.396, p < 0.001; fourth grade, R[superscript 2] = 0.745, adjusted R[superscript 2] = 0.742, F(1, 98) = 286.423, p < 0.001; fifth grade, R[superscript 2] = 0.786, adjusted R[superscript 2] = 0.784, F(1, 98) = 360.225, p < 0.001. In conclusion, the results for all three research questions indicated that NWEA projected proficiency reports are statistically significant predictors for STAAR Mathematics scores. These findings are relevant to school district administrators in Western Texas who may use NWEA projected proficiency reports to inform the process of preparing students in elementary grades for the state assessment in Mathematics. [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.]