“Separation of church and state isn’t a constitutional amendment. Ten commandments in a school isn’t establishing a religion.”
These are both untrue statements.
“Religion can be expressed in schools just like they celebrate various Christian and Muslim holidays.”
I sure hope they don’t. If you just mean giving days off so that people can either celebrate, or do whatever they want in private, then surely you see the difference.
The only holiday that might be explicitly celebrated in public schools would probably be Halloween due to the fact that nobody in America other than Jews view it as a religious holiday anymore.