"The report, leaked to Le Monde newspaper, found at least half of the 630 suburbs it looked at had already become separate ethnic communities. "
Sounds typically elitist in a snotty French way to call an ethnic community a "Ghetto".
Actually, the Muslim areas really are ghettos. The huge housing complexes were built after WW II to house hundreds of thousands of "guest workers" brought in from Morocco and Algeria to rebuild. After the 1960s, the guest workers weren't needed anymore, but because of generous French socialism, they didn't return to Northern Africa.
From what I've read, these projects were built on the outskirts of the suburbs, often cut off by highways with few bridges or access roads. They have train stops but apparently less than you would expect given the population density.
Interestingly, most French Muslims are citizens of France now; the EU rules over the past decade have made their children automatic citizens, and many of the guest workers have been naturalized.
Their schools are almost entirely Muslim. From what I've read about the school controversies, about the only thing keeping them *marginally* attached to French society is that unlike here in the US, French schools do *not* foster "multiculturalism." They have a national curriculum and national lesson plans (so that teachers day by day must teach to the same plan, everywhere.) If they did it like we do here in the US, the kids in these Muslim schools would be speaking in Arabic, doing "Muslim studies" all day long, etc. This the French will *not* allow.
What's also bad about these ghettos is that they've become major recruiting grounds for radical, jihadi Muslims (mostly wahhabists from Saudi Arabia.)