Organized matter and laws do not exist by virtue of theological claims. What makes you think such things are inherently "religious?" Is it just because a good many people attribute them to God; just because organized matter and laws concur with certain ideas deemed "religious?"
A government school is not a public forum.
I said public "context." Public schools are paid for by people from all walks of life. The law prohibits any one them to be favored or discriminated against on a religious basis. Public schools are obligated to allow religious viewpoints a hearing, whether it be in a class orientated to one of the sciences, or a class orientated toward sports.
I am arguing against government indoctrination of religion in government schools.
Allowing the presentation of certain points of view is what you call "indoctrination?" You must believe people to be weak-minded. Or maybe you think they need to be controlled lest they hear the wrong ideas. You are not arguing for free inquiry, but against it. You are free to indulge non-theistic notions by themselves in your own little school house. Once you open the doors to the public and have the public pay for them, then their views get to be heard, too, no matter how afraid you are that you and your children might be "indoctrinated."