The board of education in Toda City, north of Tokyo, has instructed schools to take thorough security measures after an intruder slashed a teacher.
Police on Wednesday arrested a 17-year-old senior high school student on suspicion of attempted murder. The student allegedly trespassed into a junior high school in the city and wounded a teacher with a knife.
The board of education said on Thursday that it had sent a written instruction to all elementary and junior high schools in Toda City.
It told schools to carefully check people when they enter and leave and to make sure that all gates and entrances are closed while classes are being held.
It also asked schools to review crime prevention manuals for strategies on dealing with intruders such as evacuating students to safety and alerting the police.
The board said it has sent additional counselors to the school where the incident took place to provide psychological care to the students from Thursday.