Under Japan’s School Education Law, local education boards can issue suspension orders to the guardians of students who repeatedly use violence at school.
However, no such suspensions were given in Tokyo in the five years through March 2011, according to the Tokyo Metropolitan Board of Education.
Looks like another classic case of Japan passing a law and sitting back while no one enforces it. See also: discrimination, child pornography, etc etc.
source: Daily Yomiuri