Effects of a Tier 2 RTI-Based Mathematics Intervention Using Evidence-Based Instruction on Decimal Division Achievement of Sixth-Grade Students at Risk

Purpose: Response to Intervention (RTI) framework by applying evidence-based instruction proven effective in the area of operations, and to empirically examine its effects on division of decimals achievement among sixth-grade students at risk for mathematics learning disabilities within the context of Level 2 support in Korea’s multi-tiered learning safety net. Methods: The participants were three sixth-grade students identified as being at risk for mathematics learning disabilities. An AB single-case research design was employed. The intervention was implemented in a small-group format over 13 sessions during after-school hours by an elementary school teacher with professional expertise. Intervention effects were analyzed using a researcher-developed assessment of decimal division achievement. Results: First, participants’ achievement during the intervention phase showed a marked improvement compared to the baseline phase. Tau-U analyses indicated very large effect sizes for all participants. Second, during the maintenance phase, the mean correct response rates remained at or above 80%, indicating that the effects of the intervention were relatively stable over time. Discussion and Conclusion: The findings suggest that a mathematics intervention based on RTI Tier 2 and incorporating evidence-based instructional practices may be effective in improving and maintaining decimal division achievement among students at risk for mathematics learning disabilities. In addition, this study highlights the importance of interventionist expertise and provides practical implications for enabling mathematics interventions delivered at Level 2 of the multi-tiered learning safety net to function as professional, Tier 2–level interventions in school settings.