This is one of the misunderstood aspects of human development, and a homeschooled child, as most people say, lacks this.  First, let me define what socialization is.


In sociology, socialization refers to the lifelong process of inheriting and disseminating norms, customs and ideologies, providing an individual with the skills and habits necessary for participating within his or her own society (http://en.wikipedia.org/wiki/Socialization).  Socialization is the means by which human infants begin to acquire the skills necessary to perform as a functioning member of their society, and is the most influential learning process one can experience.  


Let me simplify this:  socialization is a never-ending way of learning and adjusting to the culture so that an individual may be an accepted member of the society.  With this meaning alone, socialization cannot just be learned and end in school.  Does that mean when we graduate from college we are fully "socialized" so to speak?    Margaret Zysk, a homeschooling parent from Idaho, whenever people will pose their concerns about her children's interaction with other kids, she will respond, "Go to your local public school, walk down the hallways and see what behaviors you would want your child to emulate."  I love her answer so much.