The government can decide what to teach in its curriculum – it already does that. But the school library doesn't exist solely to deliver curriculum materials directly into the heads of students; it's one of the places where students are supposed to be able to explore ideas and concepts beyond their official lesson plans. The courts have ruled over and over that removing books from school libraries based on the ideas or viewpoints within is a First Amendment violation.

So to answer your question: the government can stock the libraries, or the school board can stock them, or the librarian can stock them. The courts have even said they can select books based on age-appropriateness, accuracy and educational value. But if anyone selecting books is making a judgement call about which books go in the libraries based on the ideas/viewpoints within the books, it's a violation of the students' First Amendment rights.