If you tell people not to think about elephants, they will think about elephants. And, in US schools, Jesus is the elephant.

Officially, religion has no place in the country’s classrooms. Thomas Jefferson’s declaration of a “wall of separation between church and state” paved the way for the First Amendment to the US Constitution, which states that Congress is not to make laws “with respect to the establishment of religion”, and that religion can never be “required as a qualification to any office or public trust”. When religion was thrown out of government dealings, it was therefore banished from publicly funded schools.

Despite this, American education has long been a battlefield for the fervently religious. One of the earliest conflicts played out between Roman Catholics and Protestants in 19th-century New York City. Amid fears that Catholics fleeing the potato famine were actually an army sent from the Pope to undermine the Protestant church, anti-Irish - and by extension anti-Catholic - sentiment grew across New York. Protestant educators clung to their version of the Bible and used textbooks rife with anti-Catholic statements. In 1840, concerned for the welfare of their children and already educating them at home, the Catholic community petitioned the city for a portion of common school funds.

Had the city relented, the US, like many other countries, might have ended up with religious public schools. But the people rebelled. Protesters took to the street, attacking unsuspecting Catholics and defacing St Patrick’s Cathedral. The Catholic community had no choice but to begin their own network of schools, many of which still exist today. Ten per cent of US students currently attend private schools, almost all of which are religious (and predominantly Catholic).

Despite the strict separation of church and state, however, most US citizens are religious. Recent surveys show that 77 per cent of Americans describe themselves as Christian, with more than a quarter of the population attending an evangelical church - a blanket term for institutions that prioritise the conversion of non-Christians and active promotion of a Christian lifestyle. After Christianity, Judaism and Islam are the second and third most common religions across the country, but only 3 per cent of the population identify themselves as either Jewish or Muslim. So the majority of religious battles in American education revolve around the Bible.

Against religion

For schools, the problem is that children do not shed their religious beliefs at the gates. Nor, many would argue, should students be expected to have one set of values for home and another for school. But, as public secular spaces, schools must try to encourage this.

What do you do, then, if you teach a smart 18-year-old who is your first choice for speech-giver at the school graduation ceremony? Before the event, which is not on school grounds, this young man shows you his address. He has included Psalm 146, a tale that emphasises the importance of trust in the Lord as conceived of by Christians. Would you let him give that speech?

This is the situation that Nicholas Lassonde’s school administrators faced back in 1999. After removing the religious portions of his speech at the school’s request, he filed a suit claiming that the school had violated his right to free speech, which is also enshrined in the US Constitution. Importantly, Nicholas lost. The Appeals Court for the Ninth Circuit argued that the speech would indeed have amounted to “coerced participation in a religious practice”, and if the school had allowed Nicholas to continue it would have breached the requirement to keep education and religion as separate spheres. Secularism one; religion nil.

But rulings such as this have knock-on effects. Suddenly, school football captains who led their teams in prayer before games, or students who presented in class and referred to the word of God, were in the firing line for legal petitions that claimed they were “coercing participation”. A backlash soon ensued.

In Missouri, the state where I work, the culmination of this came in 2012, when local people voted in favour of state-wide protection for the “right to pray” in schools. The state also passed a law giving students the right to refuse any homework assignment on “religious grounds”. State representative Mike McGhee quipped that students were unlikely to claim, “It’s against my religion to do algebra.” Those of us who have spent time teaching teenagers are less convinced.

The problem lies in people’s tendency to think about the precise thing they are told not to think about. Psychologists who study this phenomenon, such as David Wegner, call it the “ironic process theory”. In order to not think about something, a person must first bring it to mind, then actively banish it. However, the very process of bringing the thought to mind appears to make our brains more interested.

A consequence of ironic processing is that it can lead to hyperaccessibility, where a person trying to suppress a thought is ever more likely to recall it when they are in a stressful situation. This is the reason why brain-training computer games, all the rage a few years ago, ask people to read the word orange while saying the actual colour of the letters, blue. As players are put under more pressure, it becomes increasingly difficult to suppress the word and see the colour. Our brains instinctively make us want to shout “Orange!”, even though we know that is not what we should do.

And, in the case of religion in schools, this can lead to people becoming hypersensitive to religious ideas even when they are not intruding into school life.

Hurdle of the holidays

One notable example is that the US, it has been said, has five seasons: spring, summer, autumn, winter and “holiday”. Any teacher is lucky to make it past November without hearing the refrain “happy holidays”, if not from a child then at least from advertisements. This is partly because Thanksgiving and Christmas appear so close together in the calendar, but also because schools - and all other public organisations - need to keep the word Christmas (or Hanukkah, or Eid) off the table.

Although there are no definitive rulings on religious holidays in schools, one of the earliest test cases - Florey v Sioux Fall Schools - considered whether the singing of Christian Christmas carols was constitutional. The Eighth Circuit Court judged that if any religious festival is presented in a “prudent and objective manner”, with the focus on educating students about a specific cultural tradition rather than forcing them to observe it, then the singing of carols was a legitimate use of school time. Cue much hand-wringing.

Although students have occasionally attempted to sue choirmasters for requiring them to sing religious songs, when the work is considered to have independent artistic significance the courts’ view is that the singing of that song does not constitute a religious education and is therefore acceptable.

However, one parent’s complaint in 2008 about a two-minute nativity scene in a 22-minute Christmas production made it all the way to the Supreme Court, and was rejected only because the school demonstrated that students had also acted in the show as “ballerinas, toy doll, toy soldier, Santa Claus, jack-in-the-box, teddy bear, reindeer, Rudolph, and a mouse”. The nativity was, they argued, only one cultural object rather than a specific religious observance.

The court judgment cemented the so-called “plastic reindeer rule” - a get-out clause in which Christmas can be celebrated if a balance is provided by the use of enough secular symbols. Remember the joke about the child in Love, Actually who plays an octopus in his school’s nativity? If the film had been set in the US rather than in England, where nativity plays that emphasise the religious message of Christmas are not only legal but a beloved tradition, the octopus would not have prompted even a raised eyebrow.

Too hot to handle

Some debates, however, go beyond festivities and hit right at the heart of classroom practice. This is particularly true of the recurrent spats over the place of evolution and creationism on the science curriculum, a controversy that has plagued teachers’ planning for decades. Surveys suggest that, to avoid any difficulties, one in six US biology teachers simply avoids the topic of evolution altogether. In this case, the arguments do not hinge on keeping religion out of school but on the premise that if religion cannot be mentioned then neither can anti-religion (otherwise known as science).

This lack of willingness to teach evolution grew in part from the infamous Scopes trial of 1925. John Scopes, a Tennessee high school teacher, was required by his district to use an assigned science textbook that included a page on evolution. However, he was barred under state law from teaching that very topic. In practice, many teachers simply skipped that section of the book, but Scopes agreed to say that he taught it in order to provoke a trial.

Media interest was bolstered by the fame of the lawyers arguing the case: one was a three-time presidential nominee, the other had led the defence in the previous year’s most notorious murder trial. The case became something of a cause celebre. Though Scopes would later reveal that he had never actually taught evolution in his class, the court nonetheless found him guilty and fined him $100 (equivalent to approximately $1,300 today).

In response, many school districts removed pages referring to evolution from their textbooks. It was not until the 1960s that states began to relax the rules around educational texts; even today the dilemma is not fully resolved.

And when schools try to balance science and creationism they can still land in hot water. In 2002, one Georgia school district updated its science textbooks and decided not to remove the sections on evolution. To placate those who might complain, the district added a sticker disclaimer to the cover explaining that evolution was “a theory, not a fact”, and requesting that it be considered with the same open mind as all other scientific theories.

The move backfired. Although intended as conciliatory, the stickers prompted the American Civil Liberties Union to seek an injunction. The complaint suggested that singling out evolution for differential treatment promoted the cause of creationism. After five years of court cases and appeals, the ACLU finally got its way and the district was ordered to remove the stickers. That is an awful lot of time to spend trying to get people to not think about religion.

Which brings us back to the elephants. For a country that professes that its schools are free of religion, US educators seem to think about it far more than their counterparts in countries where Christianity is an everyday aspect of school life. The issues are never settled. Laws swerve continually back and forth, leaving schools at the mercy of the latest legal precedent and fearful that getting it wrong could result in years of litigation. Religion, it seems, has become an issue that no one wants to confront. Yet it is one that will never go away.

Laura McInerney is a PhD student at the University of Missouri, US, a Fulbright Award recipient and a former teacher in East London, England.