I know this is an old thread but I thought I'd respond anyway
The point of unschooling as I see it (and I actually tend to not call it unschooling, and prefer to call it natural learning) is that children have an endless internal desire to learn if the process is not interfered with, and that learning can occur any time. Just as they can learn to walk, talk and eat in their own time. They will learn what they need to, so they won't miss out on anything important to them. I know of unschooled children who didn't learn to read until age 11 and who are just as skilled as other children who learned at 4. What is important is that they were able to come to it in their own time through intrinsic motivation and now they have a love for it.
I don't believe that bookwork is out of place in an unschooling family, as long as it is child led. We have plenty of work books but my son is the only one who chooses when he does them. He tends to get enthusiastic about them every now and then and then he leaves them for months and practices the skills he's learned in his daily life instead. TBH most of his maths skills have been learned by asking me questions about time and money and playing with a calculator. If he asked for ore structure I'd give it to him, and I'd still call it unschooling because it would simply be me facilitating his learning for him in the way he needs me to
