Why Reformed, Christian Schools?

The title expresses a question faced by believers in various situations. Sometimes it is asked by a neighbor or fellow worker who, having sent his children to the public schools, wonders why a Christian would spend "all that money" to educate his children when it is available free. At times a student faces the question from a coworker who attends a public school. Our own sinful flesh may raise the question in order to undermine our enthusiasm for Christian education, hoping our time and money...