Instructor Visa Requires 12 years of English-spoken schooling or 12 school grades/ years?

I am wondering whether the instructor visa requires 12 years of English-spoken schooling or 12 school grades/ years? I am applying to be an ALT in Japan and the company I am applying for told me the instructor visa requires 12 years of English-spoken instruction. However, I am confused as to whether this means 12 school grades (“school years” August-May/June) or 12 years (such as attending from Jan-May/June and then starting a new grade Aug-Dec = 1 year). I am waiting for a clarification from the company and decided to post this question out there for anyone who might need it too.

by Orange-Glittering