"Grammar schools" - schools for older kids that have competitive entry requirements. Nothing else really gets the idea across in British English, even though grammar schools in the UK are 11+ Senior High / High School - nah
Then maybe it's better to stick with the Polish term "liceum"?
Educators the world over like to take revenge on people who belittle them.
Do you believe that will affect your son's matura scores? I think you're exaggerating. The name is coded and it's checked by average teachers from a different school than your son's. Even if that was the teachers of your son's school you don't criticise them but MEN.
Really, no reason to be afraid. All in all matura was criticised many times, especially the Polish language and literature part.
Press - not a bad idea except it'd be dangerous for us. Educators the world over like to take revenge on people who belittle them.
So you're at (or in?) the standoff. There's no other way to do something about it. If you fill a complaint to MEN they might snub it.