Elite education is the most cost effective way of delivering an educated elite.
The Grammar school system was based on German experience. In the late 19th Century, it was perceived that we were falling behind in technical education. What we got in response, was a watered-down German system, with the emphasis on Science tempered by aspects of the liberal education tradition. It was succeeded by an American model of universal education.
The emergent economies all have ruthlessly competitive educational systems inspired by the German model.
Panoramix's map upthread is intriguing. If you look at the Bac' results for Alsace Moselle, they are as high as Brittany, but the percentage of private schools is apparently low. There is a specific reason for this.
Perhaps the most striking of the legal differences between France and Alsace-Moselle is the absence in Alsace-Moselle of a separation of church and state, even though a constitutional right of freedom of religion is guaranteed by the French government. Alsace-Moselle is still governed by a pre-1905 law established by the Concordat of 1801 which provides for the public subsidy of the Roman Catholic Church, the Lutheran Church, the Calvinist Church and the Jewish religion, as well as providing for public education in these faiths; although parents are allowed to refuse religious education for their children. The clergy for these religions are paid for by the state. Catholic bishops are named by the President of the French Republic following proposal by the Pope. The public University of Strasbourg has courses in theology and is famous for its teaching of Protestant theology.
Local law in Alsace-Moselle - Wikipedia, the free encyclopediaCoupled with an historic connection with German educational traditions, it turns Alsace-Moselle into something of a laboratory for much of what we are discussing.