Even though they are several decades old (I think at least one was published in the 60s) I really have enjoyed reading and rereading Johh Holt's How Children Learn and How Children Fail. These books are favorites of unschoolers, but have a lot of insight that is helpful for all homeschoolers, or parents for that matter.

Also, entertainingly radical John Taylor Gatto has lots to say in criticism of compulsory schooling. He's a former teacher of the year in NY and has used this influence to take on the system.

Gatto books: http://www.amazon.com/exec/obi.....ds=john+taylor+gatto

How Children Fail: http://www.amazon.com/exec/obi.....ding=UTF8%26v=glance

How Children Learn: http://www.amazon.com/exec/obi.....26s=books%26n=507846

I also think that I've seen at least a couple of these books at the library.