The ban, passed in July following a campaign pledge made by French President Emmanuel Macron, will affect elementary and junior high schools across the country as they return from the summer break.
The new law, which went into effect on August 5, bans all types of cellphones, as well as tablets and smartwatches.
While a ban on cellphones during class hours was already in place since 2010, the new law extends to breaks and mealtimes.
Schools are free to choose themselves if they will implement the ban for students over 15. There are also some exceptions to the ban, such as for students with disabilities.
Monday is the first day that French schoolchildren under 15 cannot use their cellphones at any point during the school day, thanks to a new nationwide law.
