They at least have the excuse of history on their side, but he's it is still technically illegal. I can see that you do not understand the establishment clause.
You don't see very well nor know very much about this matter.
In God We Trust, appears behind the House speakers podium due to House Resolution 740 in 1962. Passed right after SCOTUS made their ruling concerning prayer in school and as a means of protest by the House.
It is a national motto. Get that? National motto of the nation that is the United States of America.
It has been repeatedly decided by the courts when atheists and others tried to have the motto removed from our currency that the motto does not promote a religion. The currency motto stays.
Public schools are government funded. A national motto on a government property is not promoting a religion.
Claiming a national motto is illegal makes the claimant look silly.