The mixed-method sequential explanatory research study examined the impact of implementing a block schedule in two Missouri high schools. Previously, other studies had investigated the influence of school reform on educational programming, the implementation of professional learning communities, development of project-based learning models, and the use of instructional time when teaching in the block schedule format. The purpose of this mixed-method sequential explanatory research study was to explore the impact of implementing a block schedule in relation to student academic achievement and perceived teacher attitudes in two Missouri high schools. For the study, quantitative data samples were collected by accessing archival data from each school district reflecting student standardized test scale-scores for the previously specified years (2017-18, 2018-19, 2020-21, 2021-22) in English language arts and mathematics. Qualitative data samples were collected from educators of both districts by utilizing the purposive sampling technique. This technique utilized non-probability selection methods to identify sample participants that will provide the most useful feedback or data that will be meaningful to results of the study. The researcher separated the end-of-course assessment data into multiple layers by year(s), also including a separation of achievement data for English language arts from data representing mathematics. Once separated, the ANOVA test of significance was utilized to analyze the results from both groups by examining the differences among the group means based on the standardized test scores (scale-scores) for both English and mathematics in both high schools. Upon completion of the study, it was determined that each high school was significantly impacted either positively or negatively academically because of the block schedule teaching format change. The teachers that experienced the transition in schedule format had a split opinion regarding the positive or negative effects to student learning. [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.]