Summary of Findings
So what do our three papers tell us about the question, "How many tiers are needed within RTI to achieve acceptable prevention outcomes and to achieve acceptable patterns of LD identification?" If we aggregate the results across the papers with caution, we can discern some trends. But first, let's divide our question into two parts.
"How many tiers are needed within RTI to achieve acceptable prevention outcomes?"
The Tier I data indicate students made gains and the interventions were effective, but based on low to moderate effect sizes, it would be fair to question whether enough students made large enough gains when compared to controls. The Tier II data shows students did significantly better than controls and generated moderate effect sizes (about .55) to support this finding. It would appear 50-75% of students receiving Tier II interventions responded to instruction. It was not, however, possible to determine what percentage of the total population responded in Tier II. Tier III data provided the best data for achieving acceptable prevention outcomes. The gains of students receiving both Tier II and III were significantly greater than controls and the effect sizes higher than those reported for Tier I and II. There is some data to indicate close to 40% of Tier III students made satisfactory gains. If we look at the entire student population of one of the studies, we can estimate that about 92% of students responded to either Tier I, II, or III interventions.
"How many tiers are needed within RTI to achieve acceptable patterns of LD identification?"
Regarding Tier I results there was little data reported supporting this tier alone as a means of determining special education eligibility. A review of Tier II data shows approximately 25-50% of the students receiving Tier II interventions were nonresponders. It was not possible to calculate what percentage of the total student population this represents. Tier III data from one study showed 7 out of 10 Tier III students entered special education. Data from the same study indicated about 6% of the student population participating in the three tier model was eligible for LD services.
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