Complex sentence: It is one of the most reputed schools in France, historical rival to Saint-Louis-de-Gonzague, it enrolls students from the first to the twelfth grades, and a small number of postgraduates.
Split into simpler sentences: It is one of the most reputed schools in France, historical rival to Saint-Louis-de-Gonzague. It enrolls students from the first to the twelfth grades, and a small number of postgraduates.