The Diet on Wednesday approved a bill to revise the School Education Law, giving more flexibility to the nation's nine-year compulsory schooling system by allowing schools to change curricula and how school years are divided.

The legislation passed by the Upper House will go into force in April 2016 and will allow the establishment of new nine-year "compulsory education schools."

Compulsory education in Japan is usually divided into six years of elementary school and three years of junior high school.

The new nine-year school category is expected to address concerns that the current six-year and three-year division can lead to bullying and truancy as some students face difficulties adjusting to junior high schools.

Critics also said the current division is out of synch with the physical and mental development of children today, which is said to have quickened.

To deal with such issues and to improve academic skills, some municipalities have already introduced nine-year schools integrating elementary and junior high schools. But such schools have needed special designations.

The new nine-year schools would be headed by one principal, and teachers would have to be certified to teach at both elementary and junior high schools, in principle.