Here you have some links about Summerhill, a British boarding school based on the principles of educating children in complete freedom. It was founded by Alexander S. Neill in 1921. Students choose what they want to do and learn. The fees are really expensive: from £8,568 to £14,889 per year, depending on the level (from 11,075 to 19.246 € per year).
This is the school website:
And here you have some links in English and Spanish: