I place 'religious' in quotations, of course, because, legally, the term is so ill-defined, as noted by the author. In the (in)famous School District of Abington Township v. Schempp, 374 U.S. 203, a dichotomy was created: schools could teach about the effects and the merits of religion and religious texts, but they could not promulgate the doctrines within those texts. That seems simple enough, until one considers the fact that it still doesn't give any clue as to what is meant by 'religious' and what is meant by 'secular'. All teaching will extol different virtues and abhor certain vices. Do we choose to fund education that says the Crusades were a noble and faithful attempt to save the Holy Land from infidels or one that says it was a barbarian and self-glorifying slaughter of thousands? Does the government then have the right to begin interpreting which beliefs it finds sufficiently 'religious' and which aren't? This is the first point that he considers.
The second point is, in many ways, more interesting to consider and more damning against the status quo. For any true understanding of history, science, philosophy, and the arts--in fact, for any true and well-rounded liberal arts education--one must have a deep understanding of religion. One cannot understand John Locke's Second Treatise on Government, which is the backbone of our Declaration of Independence without first understanding his First Treatise on Government. The issue? The Second Treatise's theories rest upon the First Treatise's claim that man is made equal through Adam and his progeny--a fundamentally religious belief. The argument, of course, stems off a bit, but for its full understanding, the Creation account must be considered.
And it is not simply Locke. We must understand religion (and by now, I hope it is obvious that by 'religion' I'm almost exclusively referring to Christianity) to understand the great Western thinkers: Augustine, Aquinas, Dante, Hobbes, Rousseau, Nietzsche. The list goes on and on. Some are hostile to Christian beliefs, while some are apologists. Some simply display their (and their fellows') understanding of doctrines in a given era.
What it all means is that a full-bodied liberal education must include a full-bodied education into and understanding of religious thought, and an understanding of Western thought presupposes an understanding of Christianity.
DeGirolami argues that constitutional law on religion in schools is fundamentally flawed because it is mostly piecemeal--opinions decided layer upon layer, never considering how each fits into a cohesive hole. Religion and government aims cannot be so simply separated. Government desires a populace that is civic minded, selfless, sacrificial, and 'morally responsible'. He says:
[T]he citizen must be able to think about the relevant public issue from a perspective different from his or her own and to reason about the desirability of the proposed government action from within a different world view. Teaching about religion promotes these abilities by broadening students' fund of knowledge.
Yet these perspectives, including the Supreme Court's, fail to recognize that religious learning, as part of the study of history and social studies, contributes to the conversation at the heart of civic and moral learning. (internal quotations and citations omitted)
Religious learning, then, can be beneficial to the polity as whole, leading to both an educated (and therefore more productive) citizenry and a civic-conscious people.
Now, this does not mean, he notes, that religious learning is without its difficulties. One of the ultimate problems with religious belief is that oftentimes, one of its fundamental precepts is that it should be evangelized (or, if you prefer, proselytized) to the largest possible audience. A teacher in command of teaching notions of faith may either proselytize the students for a certain belief or against a certain belief, neither of which is acceptable in a system that prizes freedom from coercion. Additionally, parents must play a role in the development of their children's beliefs, and the law must consider whether the school has any right over the beliefs of a child that a parent does not expressly condone
In the end, he concludes that
The Supreme Court has perennially reaffirmed...the core obligation of public schools is 'to teach that our strength comes from people of different races, creeds, and cultures, uniting in commitment to the freedom of all." That theme has been a cornerstone of the Supreme Court's jurisprudence of public education, and it has intimated that teaching about religion can promote that theme constitutionally, Yet in order to reconcile its sweeping and lofty statements about the virtures of civic and moral education with its Establishment Clause jurisprudence, the Surpeme Court must confront the problem of religious learning--the problem that religious learning must be, but cannot be, separated from public education--more rigorously and sensitively than is possible within its current dichotomous methodology. That binary approach--promotion or non-promotion; the "secular" or the "sectarian"--is conceptually inadequate to account for the broad and often subtle effect that religious learning has on the cultivation of civic and moral ideals....[R]eligious learning is a sphere of understandings and meanings whose particular expressions offer insights of widely divergent value for an enriched conversational engagement. To access these insights is to participate in the external and internal discursive mode of learning about and contemplating the religious voices that have come before. Liberal learning, in public schools no less than anywhere else, occurs in the perpetual achievement of tentative, temporary, and perhaps agnostic beliefs. (citations omitted)
The article is long, but it is certainly worth the read.