There is no constitutional separation of church and state. The Founders were quite clear about that. The First Amendment was to prevent the government from dictating what the people must believe or profess in religion. And it protected the right of the people to believe as they chose and worship as they chose. And that included people in government, schools, or anywhere else.
The only reason the ACLU declared war on religion was because the government paid them big bucks to do that.
In this country, the "American Rule" provides that each party to litigation is responsible to pay its own attorney's fees unless specific authority is granted by statute or a contract allows the assessment of those fees against the other party. This contrasts with the "English Rule," under which...
catholicexchange.com
So they scrounged the nation looking for any tiny religious symbol on a village, city, county seal or on a public building or historic old creches on courthouse lawns at Christmas and sued those government entities.. That was when the ACLU lost its soul and became another self serving organization instead of a champion of civil rights. And it has become so blatantly partisan and corrupt I wouldn't trust much of its opinion about much of anything.
To teach school children of the influence that religion/different religious groups have had in the migration to this 'new world', in the Declaration of Independence, in the founding documents that culminated in the U.S. Constitution, the expansion into the rest of what is now all of the USA, our art/music, architecture, values, laws, justice system that forms the culture of our country in no way violates the spirit or intent of the Constitution or the First Amendment.
