Christian schools as a genre have been around since the 1950's. Recently a subset of Christian schools known as classical Christian schools has become popular. This seems to have come about because standards in public education have steadily fallen. Many parents simply will not tolerate shoddy disciplinary standards, sloppy dress codes, violence in our schools and underachievement and low expectations. As a result they start their own schools.
A classical Christian school proclaims Jesus Christ as Lord and Savior. It also adheres to the principles of a classical education as set out by educators such Dorothy Sayers, John Milton Gregory, St. Augustine and Douglas Wilson. Parents and students enroll in a classical school because they too embrace the mission and teachings of the school. Teachers are required to sign a statement of belief as well. The result is a school community which is tightly focussed on its aims and objectives. Put another way, if you cannot subscribe to these beliefs, then you need to look elsewhere for your child's education if you are a parent.
You won't find computers and fancy technology being used in classical Christian schools. They use the trivium (grammar, rhetoric and logic). A classical Christian school seeks to produce excellent students well-schooled in their faith.
Got an aspiring hockey player in your family? Many American private schools enjoy a great reputation for excellent hockey teams as well as superb academics.
Some states do not have their own private school associations. Schools band together across state lines forming regional associations. These associations have the same purpose as state associations. More here.
Litchfield County, Connecticut, is home to a couple of dozen excellent schools catering to just about every need. The setting about 90 miles north of New York City is convenient to one of the largest metropolitan areas in the world.