It is 100% illegal to work for a high-school if you do not have you visa from them directly,

You can call the F.E.B. and ask them. I know because i have gone there in person and it is illegal also the PSB said it is illegal too.

A contract with the school does not change the law, do not eat shiit form Chinese criminals the F.E.B. is there to help you

do not risk being deported

If you give your name to the PSP they have to investigate the case and give you feed back

You can also sue within 2 years and sue them all if they take bribes and lie to you saying it is legal