You accept a job, the school sponsors your work permit, your passport goes to the consulate for the Z visa — and partway through, they tell you the role is different. By then you have resigned your old job and cannot easily back out. The salary usually does not change even though the work has.
Get the exact position, grade level and curriculum in writing as a contract annex before your permit application starts. Ask directly what happens if the role changes.
Accepted a kindergarten homeroom role; reassigned to teach IB primary ELA/Science/Social Studies across two grades — after the visa was already in process.