I'm not advocating public schools, but it's my belief that good parenting can overcome any adverse affects of public schools. Blaming schools for a child's problems seems more of a cop out to poor parenting to me.
As a possibly former teacher I can tell you it's all about parenting. The difference between a good kid and a piece of crap is almost 100% always the parents. Some teachers really are crap.. God knows I've met them, but some of them are really good and it doesn't make a lick of difference if the kid is a piece of crap, usually because of his/her parents.