Tier 2 assessments are supposed to be diagnostic assessments administered to Tier 1 non-responders to help plan interventions.
Brief overview of RTI/RTII:
Tier 1 is what every student receives. It includes the core curriculum, teacher training in proper implementation of the core curriculum/supervision of teachers for fidelity, and screening/progress monitoring to identify those students who are not making adequate progress under Tier 1.
Tier 2 comprises roughly 15-20% of students, who need additional supports beyond Tier 1 instruction. They are typically identified by underperformance on Tier 1 screeners and progress monitoring. Tier 2 assessments should tease out some of the larger causes of underperformance, and assign them to standard interventions. For example, among the low readers, there will be a subset who are not English proficient. They would be assigned to some type of ESL intervention. But unless you know that this is the type of low reader you are, it would be silly to assign all of the low readers to ESL, which is where the Tier 2 diagnostic assessments come in. Reading has been very well studied (the same cannot be said of mathematics or writing), so it is relatively straightforward to direct intervention decision-making. You need good oral language, phonological awareness, and background knowledge (context), usually listed as the Big 5 (phonemic awareness, phonics, fluency, vocabulary, comprehension). If you are lacking in one of the key elements (all of which are relatively easy to assess), one remediates that element.
Tier 3 is for the approximately 5-10% who are not making adequate progress even with Tier 1 and Tier 2 supports in place. Interventions need to be intensified and individualized. There is substantial overlap with special education, but they are not necessarily synonymous. (For example, a one-on-one mentoring relationship might be considered Tier 3, but would not require special education eligibility, nor a special educator as mentor.) Some people would insert an additional tier between 2 and 3, which would make this tier 4.
In an RTI IEP eligibility process, a student should work his/her way up through the tiers, until all appropriate non-sped Tier 3 supports have been exhausted. The information one gathers along the way, in the form of Tier 2 and Tier 3 assessments, feeds into the eligibility and instructional planning discussion. These assessments, even prior to a formal sped referral, may include tests like the PAL-II, the TOWL-4, the CTOPP/-2, the KeyMath3, and subtests of the WJIII. You probably won't get a cognitive assessment until the actual referral to sped happens. Even then, you might not get one, unless the referral question warrants it.
A 504, on the other hand, starts from documentation of disability, and some impact on a major life function. It does not require educational failure/lag. It originates from federal disability law (aka, ADA), not education, so it is not subject to the same RTI mandates (which are not federal in origin, anyway, rather imposed by the states in response to a line referencing "response to scientific, research-based interventions" as an option for LD identification).
Hmm. This got less and less brief as I went along!
