It was just like the old days, when Mississippi was burning. Freedom Riders were back on Greyhound buses – and police cars with blue lights flashing and sirens blaring were waiting for them.

This time, 50 years on, there was nothing to be scared of. Mississippi was welcoming the civil rights activists, and the police were providing an honour guard to ease their way.

Luvaghn Brown, 66, from Mississippi but now living in New York, was acutely aware of the change. "It is a huge difference. When we were escorted by the police before it was only to take us from one prison to another."

Brown was jailed in 1961, aged 16, for eating in a whites-only cafeteria and again a year later for picketing a fairground, which in those days had white-only and black-only days. He returned this week for the 50th reunion of the riders. Jackson, the state capital, marked their challenge to segregation with a week of events.

Another rider, Max Pavlesic noticed the change as soon as he arrived at Jackson's airport, and not just because it has been renamed Jackson-Evers after the slain civil rights leader Medgar Evers.

"There are only two kinds of bathrooms at the airport now, men and women," Pavlesic said. "The last time I was here there were eight: white men, coloured men, white women, coloured women, white men employees, white women employees, coloured men employees and coloured women employees. That is how outrageous the system was."

The Freedom Riders today at Mississippi State Penitentiary in Parchman

Most of the 427 riders were students in their teens or early 20s, arriving from across America on the trains and buses, black and white together going into segregated waiting rooms and cafeterias. They were attacked in Alabama and jailed in Mississippi, in Parchman, the most notorious prison in the south, William Faulkner's "Destination Doom".

They were allowed back inside Parchman this week, travelling deep into the delta in a convoy of six Greyhounds, to visit their old cells. There was a welcome placard outside the gates.

The Clarion-Ledger – which the day after Martin Luther King's 1963 "I have a dream" speech used the headline Washington is Clean Again with Negro Trash Removed – led with Riders Return as Heroes.

Governor Haley Barbour even invited them to breakfast at his mansion. A potential candidate for the Republican nomination in the 2012 presidential race, Barbour dropped out after a row over a comment sympathetic to the White Citizens Council, a civil rights era supremacist group. Some riders refused to return in protest. But Barbour surprised the 60 to 70 who did make the journey by issuing "an apology for your mistreatment in 1961" and adding: "We appreciate this chance for atonement and reconciliation."

The response of the riders was mixed, with some suspicious about Barbour's sincerity. But Hank Thomas, 70, who was almost killed when his bus was firebombed in Alabama, said: "For the govenor to apologise is a big step towards reconciliation."

Some of the riders, mainly in their 60s and 70s now, went on to become leaders of the civil rights movement. Others became teachers, lawyers, preachers and social workers. Many remain politically active, maintaining a cheerful optimism that grassroots action can achieve change and still bound by their time in Parchman.

Joan Mulholland, a retired teacher from Virginia, saw no tears when they went back to their old cells, just friends swapping stories and laughing. They had been held in Unit 17, maximum security, used for death row prisoners, even though they had been charged only with breach of the peace. The aim was to humiliate and psychologically break them. "We go to the airport now and get virtual searches. I got the real thing, [into] body cavities, which was nasty," said Mulholland, 19 at the time.

The riders angered the guards by constantly singing The Buses Are A-Coming and other freedom songs. They had their clothes taken away, their mattresses and, finally, their toothbrushes. But the songs went on. They were allowed out once a week, just long enough for a shower. They were held for, on average, about 40 days.

Claire O'Connor, 70, a community organiser from Minnesota, said it was not all bad, especially in jail in Jackson before being taken to Parchman.

"All the white women were in one cell and all the black women in another. We had a lot of fun. We studied ballet. One of the black women was a ballet teacher and shouted out instructions," she said.

She continued campaigning after Parchman, returning to Mississippi to volunteer in the African-American voter registration campaign in 1964, Freedom Summer, portrayed in Mississippi Burning.

How much of a difference did they make? One of the posters round Jackson says: "No Black. No White. Just Blues." None of the riders is naive enough to believe Mississippi is close to that. They secured an early victory for the civil rights movement, helping end segregation at bus and train stations, but they are well aware that racism is still alive in the state, as elsewhere in the US.

In parts of Mississippi, the school system is effectively segregated, with up to 99% black pupils in some schools.

Bob Filner, 68, who was jailed at Parchman and is now a Democratic congressman from California, is uneasy about the reunion posters round Jackson, "as if we have come as conquering heroes". He reels off depressing statistics about the ratio of African-Americans and Latinos in jail and the tiny proportion of African-Americans or Latinos who will make it to university. "We have a long way to go," he says.

The motives behind the reunion are mixed. It is partly a chance for Mississippi to say thanks and partly a move towards reconciliation. It is also the start of an effort to attract tourists to the poorest state in the US with the creation of a Mississippi Freedom Trail, 30 plaques commemorating landmarks in the civil rights struggle. The riders attended the unveiling of one of the first, outside the renovated Greyhound station in Jackson where some of them arrived 50 years ago.

The authorities are far from confident the plaques will not be defaced. A memorial plaque put up in the delta at the place where the body was found of Emmett Till, the 14-year-old murdered in 1955 for allegedly whistling at a white woman, has been vandalised several times.

Many young whites and blacks in Mississippi had never heard of the riders, mainly because, unlike other parts of America, the civil rights era is not covered in school. The state legislature voted this year to make it a mandatory part of the curriculum.

At a dinner in Jackson this week, tribute after tribute was paid to the riders, with African-American judges and members of the state legislature saying they would not have made it to office without their efforts. Ben Jealous, president of the National Association for the Advancement of Coloured People, speaking at the dinner, thanked the riders for having had "the foolishness to believe they could make a difference".