Reynolds and Shaywitz (2009) provides quite a scathing critique of RtI, particularly in saying there is not a lot of evidence to match the enthusiasm for RtI in terms of research support for RtI, ease of implementation, breadth of applications in the schools, and the ability of the RtI model to benefit children with learning disabilities.
The study, by Josh Wiener and colleagues at the research firm RTI International, was based on a national survey that allowed them to follow thousands of people aged 50 and over for 10-12 years.
There was much unanswered and unaddressed RtI implementation concerns as well as what the outcome research was to show the superiority of the RtI framework.