Mixed methods were used to determine teachers' and administrators' perceptions of the degree of implementation of Response-to-Intervention (RtI) in four areas: research-based and standards-driven instruction, assessment practices or monitoring, intervention strategy identification, and decision-making processes. One hundred sixteen teachers and nine administrators (N = 125) from 10 elementary schools within one urban district completed a survey to measure perception of RtI implementation. The study's findings revealed that the first two RtI implementation areas were present: research-based and standards-driven instruction and assessment practices or monitoring. The findings also showed that the third and fourth RtI implementation areas, intervention strategy identification and decision-making processes, were known; and implementation planning had begun. Further, the study's findings indicated that there were six statistically significant correlations: (1) Those who perceived a higher level of implementation in research-based and standards-driven instruction also tended to perceive the level of implementation higher in (a) assessment practices or monitoring, (b) intervention strategy identification, and (c) decision-making processes; (2) those who perceived a higher level of implementation in assessment practices or monitoring also tended to perceive the level of implementation higher in (a) intervention strategy identification and (b) decision-making processes; and (3) those who perceived a higher level of implementation in intervention strategy identification also tended to perceive a level of implementation higher in (a) decision-making processes. Finally, thematic analysis was used in the qualitative component with interviews of 12 teachers and six administrators. Five themes emerged related to characteristics of instruction, assessment instructional loop, flexible and targeted grouping, use of student data for referral process, and resources for sustaining an RtI model. [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.]