1st step: private or public (tax run)
This website focuses on public schools.
private school=shiritsu koukou/watakushi-ritsu koukou
public school=kouritsu koukou
2nd step: age
On the 2nd day of April, how old is your child?
If 6, s/he'll be in the local school called "Shou-gakkou(=grade 1 to 6)" in the April.
If 12, s/he'll be in the local school called "Chu-gakkou(=Chu-gaku=grade 7 to 9)" in the April.
If 15, mandatory education has finished.
All children can't jump classes/grades except grade 12.
3rd step: where do you live?
Grade 1 to 9 are administrated by cities/towns/villages(the smallest administrative unit in Japan).
Grade 10 to 12 are administrated by each middle-level administrative unit.
43 prefectures as "ken"
Toukyou as "to"
Kyoto & Osaka as "fu"
Hokkaidou as "dou".