Dawn in Rio de Janeiro. The traffic that clogs the city’s wide thoroughfare, Avenida das Americas, each morning has not yet built up. Only the white VW coaches carrying poor domestic servants from the favelas in the north to their employers in the south can be seen chugging along. Otherwise this roaring city of over a million inhabitants is quiet.

It’s 6.55am when 19 freshly-groomed teenagers clamber onto a rented bus that will take them out into the Brazilian countryside. Some speak quietly to each other, but most sit nervously in silence.

“The first time is horrible. You’re tense. You’re not yourself. It never works. This is my fifth time. I know what it’s like.” Paulo Sergio da Souza is a pimply 16-year-old who has played with Flamengo’s youth team since he was 10. Yet every year, he is forced to endure what has become a nail-biting tradition for every ambitious Brazilian football player. It does not matter how well Paulo Sergio played last year. If he does not perform at this year’s peneira he will be forced to leave the club.

“Cafu went through 14 different peneiras before he got a spot,” he notes. “And look where he is today. You have to be stubborn.”

The bus stops, but only so that more boys can jump aboard. One of the players falls asleep, his head nodding up and down in rhythm with the bus’s bumps. Some stare into space, others listen to their iPods. These are Brazil’s best-paid teenagers, youngsters who earn far more than the unfortunate teens who sell themselves to white tourists at the world-famous Copacabana beach. And they want it to stay that way.

The sun rises quickly above the green mountains. The thermometer already shows 28°C. Flamengo’s new training ground is in Vargem Grande, 30km outside Rio. The bus journey takes about an hour when the traffic is smooth. Otherwise it takes two.

Inside a fenced area, the youngsters get off and disappear into a narrow concrete dressing room. South America’s biggest club has called in 50 players aged 15 to 16 for the first peneira of the year. The majority are from the club’s U15 squad, but a third come from other clubs. All will be tested to see if they have what it takes to play with the U17s.

Elton is 16 and comes from Natal in the north-east of Brazil. He has travelled for three days just to be here. Last year, he was one of only two players from a group of 40 to come through a peneira at Nova Iguaçu FC, one of several feeder clubs in the Rio suburbs. Now, Elton’s agent has arranged a trial in Brazil’s most popular peneira.

“If I come through this, I’m safe. I’ll move here. My mother has a friend of a friend who I’m sure I can live with,” says Elton, tying the shoelaces of a brand new pair of Nike Total 90s, a Christmas gift from his agent. He slowly jogs towards the training facilities together with his competitors. Behind them comes the kit man, followed by the physio, the assistant physio, the masseur, the doctor, the goalkeeping coach, the assistant manager and the head coach. Each of Flamengo’s eight youth teams is coached and supervised by an eight-strong staff.

Anthony Santoro, the U17 head coach, is last onto the ground. He finds a spot in the shade under a tree. “Look,” says the 36-year-old, pointing a finger towards the 50 sweating teenagers who are running around in the heat like a bunch of scared army recruits. “On Friday there will only be 20.”

Brazil is the fifth largest country in the world, has the 11th strongest economy and is the world’s biggest exporter of iron ore, soya beans, sugar, frozen meat and orange concentrate. Last year, Brazil’s exports were worth more than US$100bn [$122bn].

Yet the money is not trickling down. Of Brazil’s 184 million inhabitants, half live in poverty. They work on the streets, with no steady income and no accommodation, polishing shoes, selling peanuts, juggling oranges, washing other people’s clothes – anything to earn a crust. The majority survive on less than three dollars a day.

Brazil’s social classes have never been so divided. Ten percent of the country’s population controls almost everything. In the UN’s most recent annual report on income, only diamond-rich Sierra Leone and Central African Republic had a wider gap between rich and poor. According to the IBGE, Brazil’s institute of statistics, wealth distribution also follows racial patterns: 86 percent of the country’s richest 10 percent are white, 12.6 percent are mixed race and only 1.4 percent are black, even though almost half of Brazilians are black.

The rich-poor divide is so entrenched that Brazil has become one of the toughest countries to grow up in. If you are born poor it is almost certain that you will die poor. The fastest way out is through talent: singing, dancing, acting or football. And of the boys, the majority choose football.

The first obstacle for these millions of potential footballers is the peneira, which means “strainer” in Portuguese. All the nation’s talents are thrown in, and out come the very best the world’s greatest football country can offer. Meanwhile, the unwanted, weak elements are left behind. It’s survival of the fittest; Darwinism applied to football.

The first peneira was held shortly after British visitors brought football to Brazil late in the 19th Century. Today, it is an industry in Brazil, with many clubs charging young hopefuls for the privilege of taking part.

The Sao Cristovao club in Rio arranges one of the most popular peneiras. At the steel gate that leads to the bumpy, worn pitch, graffiti reads: Aqui naceu o Fenomeno – “The Phenomenon was born here.”

Ronaldo had only been playing for a couple of years when, aged 13, he made it through Sao Cristovao’s peneira. Two years later, encouraged by his father who had always been a Flamenguista, he attended a trial at Flamengo. The youth coach didn’t spot his talent. Others did. Two years on, Ronaldo made his debut in the national U17 team.

Flamengo have learned from their costly mistake. Today they do not miss a thing. They would rather test 1000 hopeless cases than let slip one potential superstar.