Quite simply, Robert, why would you want your kid to spend a 35 hour week learning what he could in one day?
Well, one of the points being made here are that there is more to learn at school than just reading, writing and 'rithmatic. A lot more.
One of the big things we learned in grad school is that a very significant percentage of the knowledge we emerge with at the end of our schooling is incidental knowledge
. That's the stuff OTHER than what we learn when a teacher is teaching us. It's important in Deaf education because it's what mainstreamed deaf kids miss out on if all they're getting (via an interpreter) is what the teacher is teaching. It's what we learn from our peers, either directly or indirectly -- at recess, when the teacher is working with someone else, or just by osmosis, in a social environment (when we have access to the information, anyway).
I believe your sis is doing a good job, and I think a good job can be done.
But I think there are a lot of dangers, too.
I sent my kid to preschool to prepare her for the school experience, in general. They had an article up on their wall about how social skills when a child enters kindergarten predict future academic performance better than any other measure. Again, as littlek and Stormwatch have said, "social skills" are too often thought of as, like, please and thank you. They also include knowing how to deal with adversity -- how to react when an obnoxious kid throws sand at you, for example. When it's appropriate to try to solve a social problem yourself rather than bringing in adults. When it's important to bring in adults. Etc., etc.
Sozlet ended preschool with a love of learning and an interest in going to school. Her preschool taught her that school is a great place, where fun and interesting things happen.
She is currently jumping out of her skin with excitement as she waits for second grade to start. (After spending the summer reading a couple of shelves of books at the 4th through 10th grade levels.)