Dispatch companies employ teachers, so while they have an employer-employee relationship, the BOE (school) holds no legal relationship with the teacher. And while all workers in a school must be under the authority of the principal, in this situation, they are not. Also, if your company designates a method of teaching, but your team teacher tells you to do it another way, you could be in a position where you have to act against orders. This scenario has lead to dismissals through no real fault of the teacher. The Ministry of Education has sent a directive to all local governments telling them to stop this sub-contracting.
http://www.fukuoka-now.com/features/article_display.php?fn_code=442452