Over the years, I have on numerous occasions seen the claim that 95% of students can learn how to read proficiently, so long as they are provided adequate tier 1/2 instruction. Truthfully, it has always stuck out to me as a strange figure, for three reasons. First, most academic research does not typically use percentages in this sort of manner. Second, I often see this figure unaccompanied by a citation. And third, it seems low; I find it hard to believe that 5% of students just cannot learn how to read. That said, I have never really looked into the claim, because the general purpose of citing this figure seems to be to encourage evidence-based practices for reading instruction and this seems like a positive goal. That said, I recently saw some skepticism of the idea, based on the belief that the number is too high and that 95% of students cannot learn how to read. For this figure to have scientific validity, it would need experimental research demonstrating it to be true. Ideally, I would want to see multiple large scale studies, due to the universality of the claim. Intrigued by the discussion, I put out a public call on twitter asking if anyone had a citation for the figure. To my pleasant surprise, I was sent dozens of comments and direct messages, with links to studies and papers on the topic. 

Some of the citations I was sent were policy papers, by authors and institutions that used this claim. However, these papers were not experimental and usually cited popular Science of Reading books, not experimental research. There was also, interestingly, one research paper sent to me from the 1980s, that made the claim, but did not cite any evidence to support it. So it appears that this claim has been in circulation for a long time. The most common source listed for this claim seemed to be Louisa Moats, who has written about this rule on numerous occasions. However, she does not claim that 95% of students can reach grade level, based on just core instruction, but rather in totality. Louisa Moats cites 4 sources in support for this rule. In Kilpatrick's book Essentials of Assessing, Preventing, and Overcoming Reading Difficulties;  a 2009  paper by Lim, et al. on students with Down Syndrome; a 2005 paper by Mathes, et al, examining the rate of risk reduction for struggling reading, with intensive intervention instruction, and a literature review of risk reduction, by Joseph Torgersen. In my opinion, the last two citations provide some experimental evidence to support this claim.

The 2005, Mathes et al. paper  examined the impact of intensive reading intervention, in grade 1, on the rate of risk reduction for struggling reading. In this study classroom instruction teachers received additional instruction and struggling readers received an additional 42 hours of instruction, in small groups of 3 students. The sample included 206 studies. The study found that with this model 97% of students could read on grade level, within that school population. Mathes et al. also cited two other experimental papers that examined this issue: Mathes 2002 and Torgesen 2003. Both of these papers examined the rate of risk reduction with intensive intervention instruction in grade 1, for struggling readers. The two papers together on average showed a success rate of 96.5%. The Mathes study seemed to suggest support for the idea that 95% of students can reach grade level expectations. However, not based on only core instruction. As the students in the treatment group received 42 hours of extra instruction. 

The 2009 Joseph Torgesen paper was a literature review on risk reduction rates. He analyzed intervention studies and took the percentage of students who failed to reach grade level as defined by the 30th percentile, and multiplied that by the average rate of struggling readers in the US at the time (18%), to estimate how effective that intervention would be in preventing struggling readers if applied nationwide. The results of this analysis can be seen here: