This is an interesting question! Here is my take on the situation:
"Data" is the first key here. The language of the particular special education regulations in the state/district is the second key. The first question that should be asked is what data (i.e., CBM) is there that shows the student is not performing at grade level in mathematics? This should then drive everything else that is done. For example, if the data demonstrates that the student is not performing appropriately in mathematics in a "Tier 1" context where evidence-based mathematics instructional practices are occurring, then consideration for "Tier 2" (more intensive delivery of evidence-based instruction) may be warranted. The same would be true for Tier 2 if the student continues to struggle. Again, data (CBM) has to drive this decision as well. At the Tier 3 level, actions depend on how the district/school is implementing RTI. One option is a more intensive and different set of interventions are now implemented paying specific attention to the data results from Tiers 1 and 2. If special education is the point of tier 3 then that school/district should follow the procedures that have been outlined by their special education regulations regarding additional diagnostic testing and possible identification of a mathematics learning disability or other disability. In some cases this might mean a re-evaluation is in order. Without knowing the specifics regarding state/district special education regulations in this situation and what processes are used for identification, I would not be able to say specifically what the procedures should be. If the data collection piece is in place and has been appropriately used to match the student’s needs to the appropriate instructional interventions (i.e. Response to intervention) and the student is not responding then the "RTI" aspect has been addressed. At this point it is up to how the state/district has operationalized re-evaluation and/or disability identification procedures. In some cases, it may be logical that the language disability is the cause of the mathematics learning problems. If this is indeed the case, then a change in IEP would be appropriate to address the mathematics area without further identification. Either way, I would imagine that some diagnostic testing would be necessary to make an appropriate decision.
The crux of the matter here, in my opinion, is whether or not a student who is already identified with a disability and is receiving special education services for one content area can be automatically moved to the same delivery method for other subject areas when they begin showing difficulty but heretofore had not been. I believe the intent of RTI is to allow flexible movement of students back and forth among the instructional tiers regardless of disability identification. However, I believe movement among the tiers has to be based on data collected specific to the areas of concern. What I mean is that I do not believe the intent is to assume students who have been identified and have been having difficulty in one area "automatically" should be moved to the same level of intervention for other subject areas. Taking this approach, in my opinion, would be a violation of the principle of "Least Restrictive Environment" (LRE) and the intent of RTI as explicated within IDEA and NCLB.
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