That is not accurate. Agnosticism does not acknowledge only two possibilities. Agnosticism recognizes that there are many possibilities, including, for example, the Hindu pantheon, Roman and Greek gods, etc., in addition to the Abrahamic God.
The agnostic recognizes that there is no conclusive proof of any of them. Therefore, the agnostic cannot make a definitive statement that there is a god, many gods or no gods. The degree to which that agnostic favors one result or another is a matter of personal taste.
I think it is more accurate to say that science is non-theistic. It does not deny or accept the existence of a god or many gods. It simply does not deal with them. If it were atheistic, it would assert that there is no god or gods and that it does not do.
The argument nevertheless boils down to essentially two possibilities: material and non-material causes, or perhaps impersonal and personal causes. "Atheistic" carries pejorative baggage, to be sure, but that is a latent effect not inherent in the definition. Whatever. Neither the federal government in general nor public schools in particular have the prerogative of excluding theistic considerations, let alone non-material or personal causes, from scientific contexts. The are not empowered to establish and support atheistic principles by default.