Hundreds of French schools in deprived areas began implementing on Monday one of the key campaign promises of President Emmanuel Macron: cutting class sizes to only 12 pupils in a bid to raise standards.

Schools in designated "priority" areas around the country, where educational achievement is historically low and poverty high, have slashed their class sizes for pupils between aged five to six.

A total of 2,500 classes have been reduced to a maximum of 12 pupils instead of a current 25, as promised by Macron during his election campaign to help tackle inequality in the system.

Macron, a 39-year-old centrist elected in May, spent a few hours on Monday in class in eastern France for the first day of the new school year after the summer holidays.

According to a global ranking of education levels carried out by the Paris-based think-tank OECD, France is 27th, below Germany at 16th and far behind Estonia, which is the highest-ranked European country at third.

The research by the OECD, which tests literacy and numeracy among 15-year-olds, shows that the French system produced highly unequal results, serving high-achieving students well while failing to prepare those at the bottom.

"Twenty percent of pupils are in a worrying situation and they are mostly children from disadvantaged backgrounds," an education expert from the OECD, Eric Charbonnier, told Le Parisien newspaper on Monday.

In Corbeil-Essonnes near Paris, an AFP reporter found pupils and teachers mostly happy with the new measures at the Quatre Vents school which sits near high-rise housing blocks.

"The messing around is finished now," joked Djamel Abbas, a 44-year-old Algerian man who dropped his son off on Monday morning. "The slightest noise and the teacher will hear it."

The smaller class sizes are also expected to help teachers handle the challenge of teaching foreign-born pupils for whom French is a second language.

Education Minister Jean-Michel Blanquer has promised that the reduced class sizes model will be rolled out to cover two school years in all designated "priority" areas for pupils aged five to eight.

Polls show voters already becoming disenchanted with their new leader.

A YouGov France survey published Monday showed his approval rating falling to 30 percent in August, down from 36 percent a month earlier and 43 percent in late June.

Source: AFP