Ultimately, there is no definite answer to this. This is because each private school charges as much as they see fit. Therefore, costs and tuition prices vary by school. With that said, we can still give you the latest U.S averages:\r \r $12,350 was the average annual tuition amongst private K-12 schools \r $16,144 was the average tuition of a private high school \r $37,590 was the average cost (including tuition and room and board) of the 161 private boarding schools across the country