When students returned to Jena high school in rural Louisiana last month, they found that a broad-branched oak tree that once dominated the campus courtyard had been chopped down and turned into firewood.

Planted by the school 20 years ago as the “tree of knowledge”, it had instead become a focal point for violence between blacks and whites, as well as a symbol of the old values and racial injustice that still seem to penetrate this corner of America’s Deep South.

It all began this time last year, when black students decided that they would begin sharing the shade offered by the tree with their white counterparts, some of whom regarded it as their exclusive preserve.

The next morning three nooses were hanging from the boughs, an image intended to remind blacks of the lynchings once inflicted on their forebears. The white boys found responsible were given three days of in-school suspension after the education chiefs decided that their actions were nothing more than an adolescent prank.

But the incident prompted simmering violence between the two groups, which came to a head during the Thanksgiving holiday last November, when a fire at the school triggered a wave of fights and beatings.

Lawyers representing Mychal Bell, a 17-year-old black student, appealed yesterday to courts to set aside his conviction by an all-white jury over an incident in which a white boy was knocked unconscious. Another five black teenagers were charged with attempted murder relating to the same incident.

Two of them, Carwin Jones and Theo Shaw, had their charges reduced to aggravated assault yesterday, which means that, like Bell, they face a maximum 22-year jail sentence.

Civil rights leaders are incensed by the apparent double standards, and are planning a march through the town in support of the “Jena Six” on September 20, when Bell is due to be sentenced. They say that white youths involved in the same cycle of violence faced significantly lesser charges or have been released on probation.

One is alleged to have have pulled out a gun before Robert Bailey, a member of the Jena Six, wrestled it off him. Bailey was then charged with theft of a firearm and disturbing the peace, while the white boy escaped prosecution.

It is understood that the following Monday Justin Barker, a white student, boasted about how Bailey had been beaten up during an earlier incident when he had tried to get into a party. He was set upon by black students, including allegedly both Bailey and Bell, and was temporarily knocked unconscious. Although treated in hospital for concussion, he was well enough to attend a school event that evening.

“There’s been obvious racial discrimination in this case,” said Joe Cook, executive director of the Louisiana chapter of the American Civil Liberties Union.

“It appears that the black students were singled out and targeted in this case for some unusually harsh treatment.”

Last month Al Sharpton, the black activist, told a press conference in the town that the case of the Jena Six “speaks to a South we thought we left in the last century”.

Much of the anger is being directed at Reed Walters, the district attorney, who turned up at a school assembly flanked by police offers in the midst of initial protests over the appearance of the nooses.

Black students claim that he warned them to stop fussing, saying: “I can be your best friend or your worst enemy. With a stroke of my pen, I can make your lives disappear.” Mr Walters denies that he was looking specifically at black students when he said this, and his supporters insist that he would never prosecute someone because of the colour of their skin.

White teenagers say that the row was instigated by black athletes at the high school who felt “overentitled” and, in some cases, had been in trouble with the police before.

But Jena, a small town of about 3,500 people, does seem to have missed out on the civil rights orthodoxy that has swept most of America in the past 50 years.

Billy Doughty, the local barber, was quoted recently saying that he had never cut a black man’s hair. “The white customers, they might say something about cutting their hair with the same stuff,” he said.

Still learning

Nonwhite students make up 43 per cent of the US student body

The percentage of black students in predominantly white schools fell from 44 per cent in 1988 to 33 per cent in 2005, the lowest figure since 1968

More than a third of black pupils attend schools where fewer than one in ten students are white

The average black student attends a school where twice as many classmates live in poverty compared with schools attended by the average white student

In 1954 the Supreme Court ruled that segregation in public schools was unconstitutional. Though rendered unenforceable Alabama's Constitution still says: “Separate schools shall be provided for white and colored children”

Sources: Alabama State Legislature; Harvard University; University of California

Times Recommends

• Please help: maimed children of war want their lives back
• Cabal seizes diamond riches to buy power
• White House gatecrashers got to the president