IDEA 2004 specifies that the ability-discrepancy model and the RTI model must be used in making special education determinations while allowing states to use a third research-based model but not mandating it.
In fact, the professional literature (see Hale,School Psychology Forum, Vol. 1, Issue 1, pages 16-27, 2006) clearly states, “Neither the traditional discrepancy nor
RTI approach is sufficient for SLD identification, as the SLD definition requires
determination of whether a child has a deficit in the basic psychological processes in the
presence of cognitive integrities, which adversely affects academic achievement. Only
comprehensive evaluation of cognitive and neuropsychological processes can provide
the necessary data for practitioners to make this determination.”

The kind of comprehensive evaluation cited above is the focus of the third alternative-called the patterns of strengths and weaknesses model-that is not mandated, but allowed in states that approve it. Yet, this model was developed due to the flaws of the other two models. For example, the age-old discrepancy model may be unduly influenced by the fact that information processing/executive functioning deficits affect cognitive scores in a downward direction, preventing there from being a discrepancy in an other wise learning disabled student. The third model accounts for problems like this by comprehensively analyzing processing disorders and accounting for them by not using measures like the full scale IQ which are affected by these deficits and using the indices measuring these strengths and weaknesses themselves. While ability-achievement discrepancies can be helpful at times, the more distrubing problem is when no discrepancy can be found because of the downward influence on cognitive scores by processing deficits, making students ineligible. So, why are we not recognizing what has been know in the professional literature for awhile? I believe about 21 states do. but for those that do not, these students are ata disadvantage.