This quantitative study investigated current data-based instructional decision-making (DBIDM) practices of K-3 general education teachers implementing a MTSS/RTI model to address students' academic needs. A thirty-item electronic survey was designed to examine and measure aspects of K-3 general education teachers' formative data use and perceptions in relation to their DBIDM practices including their experience, knowledge, training, school-based supports, and the impact on student learning. Data were obtained from K-3 general education teachers within 35 primary and elementary schools across four South Carolina school districts identified as implementing RTI district-wide (in all primary and elementary schools) and school-wide (at each grade level). The findings demonstrated that teachers' measurement and evaluation practices varied greatly, relying on informal and unsystematic measures of student progress, more often than formative evaluation using CBM, within Tiers 1 and 2 of RTI. In addition, despite the availability of various school-based supports, teachers reported time as a major barrier to their ability to use data to guide instructional decision-making. The findings also demonstrated a statistically significant relationship between teachers' reported DBIDM practices within Tier 1and perceived preparedness for all aspects or steps of progress monitoring, as well as perceived impact on student learning outcomes. The implications for both practice and research are discussed. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]