This is a rantey-subject I've been looking forward to bitching about for a while, and, ideally, I won't blow it too badly. I'm homeschooled. Well, unschooled, I suppose. I spend my days doing things that entertain me; posting on webboards, IRCing, listening to music, gaming, reading, coding...Whatever strikes me as fun at the time. It goes in phases, actually: rarely do I go from 'gaming' to 'coding' to 'reading' within a single day. Instead, I'll typically focus on a single thing for a good 10-20 hours, burn out, and repeat the process with one of the others.
Public school is flawed. For whatever reason, it's not about education, nor has it been anytime within my lifetime. I've heard some people have decent schools; maybe they just suck more out in Oregon. The approach to teaching around here seems to be "force-feed and regurgitate": read chapters X, do homework Y, take test Z. It might work if the student has an active desire to learn the stuff and takes the time to comprehend and learn it. They can get by without, however, and the material is typically presented as highly disinteresting. Why should they bother?
Over the years, curiosity in new things drops off to about nill. Learning for its own sake ceases to be fun and interesting for many people, as they associate it with the unpleasant and forced nature of school. Somewhere along the line, they develop a dependance on the system; "it's the only way to learn". The most common comment I seem to get is "without school, how will you learn to do $foo?".
I'm not too hot on what little I've heard about most private schools, either, for basically all the reasons that've been mentioned by others within this thread. It might be a viable alternative, but it seems like they could easily just have the exact same problems.
The key thing in learning, I think, is having the kid be interested in it. If they don't care or are actively resisting, why bother wasting your time? Provide motivation, keep them interested, keep them involved.
I suppose the private vs public vs home/un thing is really a question of values. What do you define as "learning"? Is learning more important than money? How much should they learn in what span of time?
The only increased cost that I can see in (home|un)schooling would come from having to take care of the kid(s) during the day when they're young. Teach 'em to cook eggs, pasta, and sandwiches before they're 8 and let 'em fend for themselves. Well, maybe enlighten them on reading, walking, and the route to the library, too.
Admittedly, there are downsides: it's pretty much impossible to get a "well-rounded education" out of unschooling, and the dating prospects are typically about nill.
I don't have any references to cite, but A.S. Neil started a <a href="http://www.s-hill.demon.co.uk/">pretty nifty-looking private school</a> in England, and wrote <a href="http://www.amazon.com/exec/obidos/tg/detail/-/0312141378/qid=1040578605/sr=8-1/ref=sr_8_1/104-3785129-2275964?v=glance&s=books">a book</a> about it. Lots of books have also been written about home/unschooling, but I've only ever read <a href="http://www.amazon.com/exec/obidos/tg/detail/-/0962959170/qid=1040578205/sr=8-1/ref=sr_8_1/104-3785129-2275964?v=glance&s=books">this one</a>.
--Sk