“We have to absolutely talk about this,” said Mr. Nahon, 51. “We cannot continue as we did.”

In theory, laïcité promotes egalitarianism, keeping religious belief private. But critics say that in practice it has become a pretext for exclusion and discrimination.

Benoist Apparu, a legislator and former secretary of state for housing, said the law was outdated. “We’ve got to stop with this secular totalitarianism,” he said. Reforming the law “should not be taboo,” he said. “We need to accept the debate.”

Youth living in the suburbs “see laïcité as a way to push them away,” said Louis-Georges Tin, president of the French Black Coalition and République & Diversité, a research body. “In recent years, it has become a way to discriminate between Muslims and Christians,” he said. Muslim students may not wear head scarves, he said, but some schools hold Mass every day, and nearly every French state holiday is a Roman Catholic holy day. Halal food is not permitted in school canteens, though nonpork meals are often available, but schools can offer fish dishes on Friday. “Either you allow everything, or you ban everything,” Mr. Tin said.

Mr. Nahon acknowledged the discrepancies. While he supports a strict application of laïcité, the school adheres to the Catholic liturgical calendar and holds Christmas parties every year, and students eat crepes for Mardi Gras and chocolates for Easter.

Laïcité was formalized in the 1905 law, which since has meant that churches and synagogues built previously are state property and maintained by public funds. But Islam came later, mosques get no state funding, and the state has struggled to apply laïcité to public schools, beaches and sports halls. (Alsace-Lorraine, German in 1905, operates under the Napoleonic Concordat that allows religious education but does not include Islam among the religions that are studied.)

Regulations aimed at Islam have increased. A law banning head scarves (and other religious symbols worn conspicuously) in public high schools was passed in 2004. Another law banning the full-faced veil in public spaces was passed in October 2010.

Women are also banned from wearing head scarves while accompanying students on school trips if they “perturb scholastic activity.” Minarets, typically part of a mosque, are rarely allowed. Overcrowded mosques have forced Muslims to pray in the streets, which Marine Le Pen of the conservative National Front has likened to the Nazi occupation — and an occurrence mayors have the authority to ban.