This site link below is a government-approved information website for studying in Japan, operated by the Japan Student Services Organization in cooperation with the Ministry of Education, Culture, Sports, Science, and Technology and the Ministry of Foreign Affairs.

This link is the guide for higher education.

https://www.studyinjapan.go.jp/en/planning/educational-system/

School Choice Japan is for parents of younger children.

Till grade 9 it's mandatory.

All children can't jump classes/grades except grade 12.