The hothoused children even out to where they should be in school when they move from learning to read to reading to learn.
I think it's also due to the
appearance of evening out. By third grade, most kids can read a simple chapter book, giving an appearance of evening out. This is because because most third graders aren't asked to read, say, a novel. There aren't a lot of opportunities to read novels in third grade, so a child who can reads novels at home or under his desk won't stand out as much. Plus, and this is really important, third grade teachers don't measure comprehension of novels. Hence the appearance of everyone being at the same level.
Contrast this to kindergarten. Any kid who can read with any degree of fluency will stick out like a sore thumb, and there are multiple opportunities for a Kindergartner to demonstrate her abilities. She can read the directions on a worksheet, the title of the books on teacher's desk, her apple juice carton, and so on.
Val
