A continuing focus for American Education is to bridge, lessen, and eliminate the persistent achievement gap that has existed for over 50 years. Due to mandates of the Every Student Succeeds Act (ESSA), each state currently creates an individualized plan to narrow the gap. This study allowed for understanding of how the percentage of the total amount of received funds within different funding domains predict student achievement. This study specifically examined Comprehensive Support Improvement and Targeted Support Improvement allocated funds provided through federal Title 1 1003 funds mandated through ESSA within a state designated framework. Within this longitudinal, ex post facto quantitative research study, a hierarchical linear statistical model was used to create a growth model of change in test scores over five years and test the funding domains as predictors of student achievement. A second study utilized a survey of Comprehensive Support Improvement and Targeted Support Improvement school principals to explore how best practice use might mediate the relationships between funding allocation domains and achievement. Within RQ1, spending on curriculum and instruction was a significant predictor of a reduced gap in mathematics achievement for both American Indian/Alaska Native and economically disadvantaged subgroups prior to potential outliers being removed. Year was also a statistically significant predictor in mathematics achievement for both subgroups, yet ironically for predicting an increase of the achievement gap. However, the curriculum and instruction effect was no longer significant after the potential outliers were removed. For RQ2 and RQ3, no variables were significant predictors of achievement gap reduction or high performance, best practice implementation, however, this study allowed for insights, conversations, and a springboard into future research studies. [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.]