In terms of identifying students with specific learning disabilities (SLD), RTI was proposed as an alternative to the ability–achievement discrepancy model, which requires children to exhibit a significant discrepancy between their ability (often measured by IQ testing) and academic achievement (as measured by their grades and standardized testing). Methods to identify students with SLD have been controversial for decades and proponents of RTI claim that the process brings more clarity to the Specific Learning Disability (SLD) category of the Individuals with Disabilities Education Improvement Act (IDEA 2004), while opponents claim that RTI simply identifies low achieving students rather than students with learning disabilities.