Battle of the Classes 2019 La Lutte des classes

As everyone knows, children make no difference between social classes, skin colors or religions. But then why does Corentin, Paul and Sofia's nine-year-old son, only have friends like him at Bagnolet's school? And when his friends all leave for a private school in Paris, his parents are frightened. From now on, Corentin is the only one in his class. But the only what?