The evidence in support of the first assumption is compelling. Williamson (2006, 2008) has undertaken extensive analysis of the level of complexity and difficulty in the texts required in high schools and college. Measuring complexity in Lexile levels, he found that the gap between 12th grade (1220L) and the first year of college (1350L) is about 130L. The typical grade-to-grade increase in the secondary years is about 50L; thus, if we want students to enter college or the workplace ready for the texts they meet, we will have to close about an 80L gap, or about 1.6 grade levels, on a readability scale.
OK, if we'd start increasing the complexity by 10 points in 5th grade, and continue building between 5th and 12th grade so that there would be a 60 point increase in complexity each year instead of 50, that would be sufficient to close the gap, right? So why are we raising expectations in early elementary reading?
Also, if this is all so neatly quantifiable, can't we also phase it in over eight years so that nobody has to deal with a sudden jump in complexity, since the entire premise is that a big jump in complexity (in college) is bad?
Or maybe all these numbers aren't nearly as precise or useful in practice as they are in constructing academic studies.