I'll say it worked great for me who struggled with bullies and traditional school systems for whatever reasons. I later went on and got a GED (took all the tests in one day and did very well). Later went on I went to a community college and then state university finished with a BS in CS.
For me things tend to be much easier to understand if I need to understand it in order to solve a problem and then I could go as deep into a topic as necessary. For example if someone had told me that geometry and trigonometry were what I needed to know to be able to 2D game graphics and presented it in the context of game programming I would have been a million times more interested. I was definitely one of those kids who asked "why do I need to know this?" And typically the answer was not forthcoming, even though being older I understand this much more clearly.
Also, I'll add that I don't know that you have to necessarily cram a bunch of information into a kid just because they're a kid. If they learn how to learn and later on need it, you can still be quite well equipped to learn more. In fact it seems easier to me as you get older and have more context around all subjects.
Any pointers on how to manage the ubiquitous devices we find ourselves preoccupied with these days? Maybe this is more of a general kids question than an unschooling one :)